LONDON (Reuters) - A massive bomb shattered Norway's main government building in Oslo on Friday, killing two people, police were quoted as saying by local news agency NTB.
There was no claim of responsibility, though NATO member Norway has been the target of threats, if not bombs, before, notably over its involvement in conflicts in Afghanistan and Libya. Prime Minister Jens Stoltenberg was safe, NTB said.
Here are details of some of the Islamist militant groups with a record of links to plots in Europe.
* AL QAEDA:
-- Al Qaeda is seen as the militant group that poses the more serious international threat because it is has highly experienced bombmakers and a long-established transnational networks of financial, logistical and ideological support.
-- Though the militant group led by Osama bin Laden was weakened after the 2001 U.S. invasion of Afghanistan, it has survived by deepening its alliances to local militants in the Afghan-Pakistan border area where he is believed to be hiding and by cultivating affiliate groups in other regions.
-- In an audiotape released in January 2010, bin Laden claimed responsibility for the December 25 attempted bombing of a U.S-bound plane and said it was a continuation of al Qaeda policy since the September 11 attacks.
* ISLAMIC MOVEMENT OF UZBEKISTAN:
-- The IMU emerged from the Fergana Valley in Uzbekistan and has also fought in Tajikistan, Kyrgyzstan and Afghanistan with the aim of establishing an Islamic Caliphate.
-- With many of its supporters holed up in the tribal areas of Pakistan, it has forged close links with al Qaeda.
-- Earlier this month intelligence sources said there was a plot against European targets reportedly originating with a group in mountainous northern Pakistan, some of them believed to be European citizens.
-- One security official in Germany said word of the plot had probably come from the interrogation of a German-Afghan suspect in Afghanistan. The suspect was identified by media as Ahmed Sidiqi, a German of Afghan origin and IMU member.
- German media said he came from Hamburg and had been held in the U.S. military prison of Bagram in Afghanistan since July.
-- Counter-terrorism expert Guido Steinberg said Sidiqi was a member of a cell of militants from Hamburg that was believed to be a central component of the conspiracy and he said that the cell left for Pakistan in March 2009 and joined the IMU.
-- Lashkar-e-Taiba (LeT) and Jaish-e-Mohammed are militant groups based in Pakistan's Punjab province and once nurtured by Pakistan's Inter-Services Intelligence (ISI) agency to fight India in Kashmir. They have since been banned.
-- Western security sources say both are obvious points of contact for Europeans traveling to Pakistan seeking help to travel to the tribal areas to join up with al Qaeda.
-- Lashkar-e-Taiba, blamed for the attack on Mumbai that killed 166 people, has generally focused on Kashmir and India, though it has been linked in the past to some plots in the west.
-- David Headley, an American arrested in Chicago in 2009, has pleaded guilty of working with Lashkar-e-Taiba to plot attacks in India, including surveillance of targets in Mumbai.
Headley is also charged with plotting a revenge attack on a Danish newspaper that published cartoons depicting the Prophet Mohammed in 2005.
-- LeT's humanitarian wing, the Jamaat-ud-Dawa, enjoys support in the Pakistani diaspora and security sources have said they feared LeT could exploit this network to facilitate an al Qaeda-inspired attack on the west.
-- Jaish-e-Mohammed has also been linked to plots in the west. It is seen as closer to al Qaeda than Lashkar-e-Taiba.
* AL SHABAAB:
-- Al Shabaab, which means "Youth" in Arabic, has taken control of large areas of south and central Somalia. The Horn of Africa nation has been mired in anarchy since warlords toppled military dictator Mohamed Siad Barre in 1991.
-- Somali officials said the bomber who killed 22 people, including three government ministers, at a graduation ceremony in December 2009 was a 26-year-old Danish citizen of Somali descent. One of the bombers that struck an African Union base in September 2009 was reportedly from Seattle, while about 20 young men were said to have disappeared from Minneapolis's large Somali community in the last two years to join al Shabaab.
-- Shabaab's external reach has been highlighted after January 2010's attack on cartoonist Kurt Westergaard in Copenhagen, as well as its pledge to support Yemeni insurgents linked to al Qaeda who are believed to be behind the foiled Christmas Day bombing of a commercial airliner over Detroit.
-- It also claimed responsibility for the attack in Uganda in July 2010 when bombers killed 79 people in Kampala at venues packed with fans watching the World Cup final.
-- The Tehrik-e-Taliban Pakistan (TTP), or Pakistani Taliban, is the group most influenced by al Qaeda and focuses on attacking the Pakistani state, which it considers illegitimate.
-- The TTP claimed responsibility for an attack in Mohmand, a Pashtun region on the northwestern border with Afghanistan which killed 102 people and wounded at least 80.
-- Earlier this month a British man, Abdul Jabbar, reportedly killed by a U.S. drone strike in Pakistan, had ties with the would-be Times Square bomber, Faisal Shahzad, a Pakistani intelligence official said. The man had also been in the process of setting up a branch for the Taliban in Britain.
-- The TTP in September had threatened attacks on the United States and Europe. Shahzad was the closest it came to success.
-- Led by Abdelmalek Droukdel, AQIM burst onto the public stage in January 2007, a product of the rebranding of fighters previously known as Algeria's Salafist Group for Preaching and Combat (GSPC).
-- The Salafists had waged war against Algeria's security forces but in late 2006 they sought to adopt a broader jihadi ideology by allying themselves with al Qaeda.
-- Security officials were particularly concerned that rebels, who belong to AQIM, could use cash from drug smuggling to recruit new fighters and finance violent attacks.
-- U.S. officials have said traffickers use the Sahara as a staging post for flying illegal drugs from South America into Europe and that AQIM could also tap into the smugglers' network of aircraft and secret landing strips.