* Taylor convicted by special court
* Rights groups, victims welcome judgment
* Sentencing expected next month (Adds White House comment)
By Thomas Escritt and Anthony Deutsch
THE HAGUE, April 26 (Reuters) - A United Nations-backed court convicted former Liberian president Charles Taylor of war crimes and crimes against humanity, the first time a head of state has been found guilty by an international tribunal since the Nazi trials at Nuremberg.
The first African leader to stand trial for war crimes, Taylor had been charged with 11 counts of murder, rape, conscripting child soldiers and sexual slavery during intertwined wars in Liberia and Sierra Leone, when more than 50,000 people were killed.
The warlord-turned-president was accused of directing Revolutionary United Front (RUF) rebels in a campaign of terror to plunder Sierra Leone's diamond mines for profit and to obtain weapons.
On Thursday, the court ruled that Taylor, 64, was criminally responsible for aiding and abetting the crimes, and found him guilty of providing weapons, food, medical supplies, fuel and equipment to forces in Sierra Leone that committed atrocities.
But it said he was not guilty of either ordering or planning the atrocities - a disappointment for the prosecution and a decision that could eventually result in a lighter sentence.
"The trial chamber, having already found the accused guilty of aiding and abetting, does not find the accused also instigated these crimes," Presiding Judge Richard Lussick said.
Wearing a dark blue suit and maroon tie, Taylor looked calm and subdued as the presiding judge took more than two hours to read out the charges, evidence and final ruling.
The litany of gruesome crimes covered rapes and enslavement, beheadings and disembowelings, amputations and other mutilations carried out by child soldiers notorious for being high on drugs and dressed in fright wigs.
"A civilian was killed in full public view and then his body was disemboweled and his intestines stretched across the road to make a checkpoint. Women and children were raped in public, people were burned alive in their homes," the judge said.
"The purpose of these atrocities was to instill terror in the civilian population."
And in return for providing arms and ammunition for the conflict, the judge recounted how Taylor had received "blood diamonds", as the stones from Sierra Leone's conflict zones were known, including a 45-carat diamond and two 25-carat diamonds.
The trial attracted international attention, not just because of Taylor himself but because supermodel Naomi Campbell was called as a witness by the prosecution in an attempt to show that Taylor was knowingly trading weapons for diamonds.
The prosecution said Taylor had sent uncut diamonds to Campbell's hotel room after a dinner given by Nelson Mandela, attended by both her and Taylor. She told the court she had no idea who had sent her the diamonds, which she called "dirty little pebbles".
Human rights groups and victims welcomed the court's decision, with some saying it would serve as a strong warning to other leaders responsible for atrocities in conflict zones.
"Taylor's conviction sends a powerful message that even those in the highest-level positions can be held to account for grave crimes," Elise Keppler, senior counsel for Human Rights Watch, said in a statement.
"Not since Nuremberg has an international or hybrid war crimes court issued a judgment against a current or former head of state. This is a victory for Sierra Leonean victims, and all those seeking justice when the worst abuses are committed."
White House spokesman Jay Carney said: "While there is no way fully to redress the suffering and loss of those who were killed, tortured, raped, and enslaved in the service of Taylor's criminal schemes, we are hopeful that today's ruling will help to dissuade others who might follow in his footsteps."
He said in a statement that the court "sent a clear signal that neither rank nor title will shield from justice those who perpetrate the most egregious of crimes."
A sentencing hearing is scheduled for May 16, with a decision expected later that month.
Court sources said the judges had earlier been in disagreement over the verdict and were not speaking to each other at the end.
Carsten Stahn, professor of international criminal law at the University of Leiden, said the decision to convict unanimously was a surprise.
"There have been rumors of conflicts between the judges in the trial chamber, which is partly why it's taken so long to reach a verdict," he said.
El Hadji Malick Sow, who as alternate judge sat through the six years of the trial but was excluded from deliberations, sought to express a dissenting opinion at the end.
"The guilt of the accused from the evidence provided in this trial is not proved beyond reasonable doubt," he said, remaining in the chamber after his colleagues had left and his microphone had been switched off.
Victims were in no doubt about the conviction.
"I'm so happy that justice has been done," said Alhaji Jusu Jarka, 46, who had both hands amputated during an attack on Freetown on Jan. 6, 1999.
Standing outside the special court in Freetown, he told Reuters he hoped Taylor would get "100 or more years" when sentenced.
Taylor has denied the charges, insisting he tried to bring peace to the region and arguing his trial was a politically motivated conspiracy by Western nations.
But the judge said that "the accused was publicly promoting peace, while privately providing arms to the RUF," adding that "There was a constant flow ... of diamonds from Sierra Leone to the accused, often in exchange for arms and ammunition."
Liberian Senator Sando Johnson, a family spokesman, said: "We will not give up in this fight and we will not give up this struggle. We are going to stand by Mr Taylor until death do us part."
At the start of the hearing, Taylor seemed relaxed, waving at some people sitting in the public gallery, and separated from the windowless trial chamber by a thick pane of glass.
Later, as the presiding judge's reading of the judgment appeared to swing against Taylor, the former president clasped his hands more tensely in front of him.
Taylor, a former Baptist who converted to the Jewish faith, is one of just a handful of former leaders who have appeared before the international courts.
The International Criminal Court, also in The Hague, is pursuing several investigations with mixed success.
Last year it arrested former Ivory Coast president Laurent Gbagbo, who is charged with individual responsibility on counts of crimes against humanity -- murder, rape and other forms of sexual violence, persecution, and other inhuman acts.
It issued an arrest warrant for Saif al-Islam Gaddafi, son of the country's late leader, but is caught in a battle with the Libyan authorities over where Saif, who was captured last year but remains in Libyan hands, should be tried.
Former Yugoslav president Slobodan Milosevic died in The Hague in 2006 before the war crimes tribunal for former Yugoslavia could reach its verdict.
The Taylor case was closely watched for its security implications, with a U.S. diplomat warning in the WikiLeaks cables that if Taylor was acquitted or given a light sentence, his return to Liberia could threaten "a fragile peace".
Taylor's trial was moved to The Hague in June 2006 due to fears that a trial in Sierra Leone's capital Freetown could kindle unrest in Sierra Leone or Liberia. (Additional reporting by Simon Akam in Freetown, Clair MacDougall and Alphonso Toweh in Monrovia, Bienvenu Bakumanya in Kinshasa and Matt Spetalnick in Washington; Writing by Sara Webb; Editing by Alison Williams, Giles Elgood and Philip Barbara)
Judges at the Special Court for Sierra Leone said Taylor played a crucial role in allowing the rebels to continue a bloody rampage during that West African nation's 11-year civil war, which ended in 2002 with more than 50,000 dead. Ten years after the war ended, Sierra Leone is still struggling to rebuild.
The rebels gained international notoriety for hacking off the limbs of their victims and carving their groups' initials into opponents and even children they kidnapped, drugged and turned into killers. The rebels developed gruesome terms for the mutilations that became their chilling trademark: They would offer their victims the choice of "long sleeves" or "short sleeves" - having their hands hacked off or their arms sliced off above the elbow.
The 64-year-old Taylor will be sentenced next month after a separate hearing.
The court has no death penalty and no life sentence. Judges have given eight other rebels as much as 52 years in prison.
The verdict was hailed by prosecutors, victims and rights activists as a watershed moment in efforts to end impunity for leaders responsible for atrocities.
The ruling "permanently locks in and solidifies the idea that heads of state are now accountable for what they do to their own people," said David Crane, the former prosecutor who indicted Taylor in 2003 and is now a professor of international law at Syracuse University. "This is a bell that has been rung and clearly rings throughout the world. If you are a head of state and you are killing your own people, you could be next."
U.N. Secretary General Ban Ki-moon hailed the judgment as "a significant milestone for international criminal justice" that "sends a strong signal to all leaders that they are and will be held accountable for their actions," said U.N. deputy spokesman Eduardo del Buey.
U.S. State Department spokeswoman Victoria Nuland said Taylor's prosecution "delivers a strong message to all perpetrators of atrocities, including those in the highest positions of power, that they will be held accountable."
Despite optimism over the verdict, international efforts to prosecute leaders have been spotty at best. Slobodan Milosevic died in his cell before a verdict could be reached on charges of fomenting the Balkan wars. Moammar Gadhafi was killed by rebels last year before he could be turned over for trial. Sudanese President Omar al-Bashir is openly defying attempts to arrest him on international genocide charges.
In one success story, prosecutors at the U.N.'s Yugoslav war crimes tribunal are close to wrapping up their case against former Bosnian Serb leader Radovan Karadzic - although it took more than a decade to have him arrested.
The global implications meant little to survivors of the war in Sierra Leone who celebrated Taylor's conviction.
"I am happy that the truth has come out ... that Charles Taylor is fully and solely responsible for the crimes committed against the people of Sierra Leone," said Jusu Jarka, who had both his arms hacked off by rebels in 1999 and who now runs a support group for fellow amputees.
Crowds that gathered to watch the verdict live on television in the Sierra Leone capital, Freetown, sighed with relief when the conviction was announced. Some carried posters that exposed still-simmering anger. "Shame on you Charles Taylor. Give us your diamonds before going to prison," one read.
Prosecuting Taylor proved how hard it is to bring leaders to justice. He fled into exile in Nigeria after being indicted in 2003 and wasn't arrested for three years. And while the Sierra Leone court is based in that country's capital, Taylor's trial was staged in the Netherlands for fear it could destabilize the region.
There was no clear paper trail linking Taylor to rebels, and the three-judge panel wound up convicting him of aiding and abetting the fighters. He was cleared of direct command responsibility over the rebels.
In their verdict, reached after 13 months of deliberations, the judges said Taylor regularly received diamonds from rebels. But they made no mention of the most famous witness to testify about the gems - supermodel Naomi Campbell, who recalled being given a bag of "very small, dirty-looking stones" at a 1997 dinner at Nelson Mandela's official mansion in South Africa.
Taylor attended the dinner, and prosecutors had hoped Campbell would testify that he gave her the diamonds. But Campbell did not, and Taylor's lawyer, Courtenay Griffiths, dismissed the testimony on Thursday as "a large, fat zero."
Taylor, impeccably dressed as usual in suit and tie, said nothing in court and showed no emotion as the verdict was read.
There was emotion enough during the five-year trial as 91 prosecution witnesses outlined the horrors of Sierra Leone's war, many of them describing murders, mutilations, torture and acts of cannibalism by rebels and the children they turned into merciless killers.
Taylor insisted he was an innocent victim of neocolonialism and a political process aimed at preventing him from returning to power in Liberia. In seven months of testimony in his own defense, he cast himself as a peacemaker and statesman in West Africa.
Crane - a vocal supporter of efforts to hold leaders accountable - concedes that while war crimes tribunals are independent, they are hard to separate from geopolitical realities.
Syrian President Bashar Assad's regime is widely accused of atrocities as it battles to put down a popular revolt, and yet the prospect that he or any of his generals will be indicted anytime soon appears remote. Syria does not recognize the International Criminal Court, meaning prosecutors there cannot intervene unless the U.N. Security Council asks them to. Russia and China would likely veto any such move.
The ICC has indicted al-Bashir for genocide in Darfur, Sudan, but he has openly defied an international arrest warrant by flying to friendly nations and has recently cranked up war rhetoric in his country's border dispute with South Sudan.
Most likely the next former leader to face justice will be former Ivory Coast President Laurent Gbagbo, who is jailed in The Hague on charges of attacking political opponents as he attempted to cling to power following elections last year.
Edward Songo Conteh, of Sierra Leone's Amputee and War Wounded Association, was in court Thursday to watch the verdict. His only regret was that Taylor was not immediately sentenced.
"I want to see this man behind bars for the rest of his life," said Conteh, who had one of his hands hacked off by child soldiers.
Associated Press writers Clarence Roy-Macaulay and Jessica Mcdiarmid in Sierra Leone contributed to this report.