* Woman in jail with legs shackled, activists say

* Lawyers have launched an appeal

* Previous stoning sentences were not carried out

By Alexander Dziadosz

KHARTOUM, May 31 (Reuters) - A Sudanese woman, believed to be around 20, has been sentenced to be stoned to death for adultery, and is being held near Khartoum, shackled in prison with her baby son, rights groups and lawyers said on Thursday.

Campaigners condemned the ruling, saying it violated international standards and raised concerns that Sudan might start applying sharia, or Islamic law, more strictly following the secession of mostly non-Muslim South Sudan last year.

The woman, Intisar Sharif Abdalla, was sentenced by the Ombada criminal court on April 22, court documents seen by Reuters showed.

Two lawyers assigned to her case, who declined to be named, said they were launching an appeal adding Abdalla appeared to be under severe psychological strain.

"She's in dire need of a psychiatrist because she appears to be in a state of shock from the social and family pressures she's under," one lawyer said.

Abdalla was illiterate and did not have a lawyer or interpreter in the courtroom, although Arabic is not her native language, the lawyers and activists added.

Arabic is the main language in the overwhelmingly Muslim nation, though a wide range of smaller languages are also spoken, particularly in tribal areas. It was unclear where Abdalla came from.

Officials in Sudan's justice and information ministries said they could not immediately comment on the case when Reuters contacted them by phone.

Abdalla's exact age has not been confirmed, but activists said she was believed to be around 20, although some reports indicated she could be younger.

"The case certainly raises concerns about how judges are interpreting and applying the laws of Sudan," Jehanne Henry, a senior research at advocacy group Human Rights Watch, said.


ISLAMIC LAW

Floggings are a common punishment in Sudan for crimes like drinking alcohol and adultery. But sentences of stoning are rare.

Following a 1989 coup, Sudan introduced laws that took sharia as their main source and hosted militants including Osama bin Laden.

While the government has since sought to improve its image internationally by distancing itself from radical Islamists, it is still one of only a few countries to list death by stoning in its statutes.

In 2010, Sudan's President Omar Hassan al-Bashir said the country would adopt a fully Islamic constitution following the secession of the south, agreed under a 2005 peace deal that ended decades of civil war.

Most people in South Sudan are Christian or follow traditional African beliefs.

The Strategic Initiative for Women in the Horn of Africa (SIHA), a network of civil society groups, said Abdalla was still in danger despite the appeal.

"Although this appeal is in process, Intisar ostensibly remains at risk of being stoned and in real terms, her life is still very much on the line," it said in a statement.

In 2010, the case of Lubna Hussein, a Sudanese U.N. official, sparked international furore when she was sentenced to flogging for wearing trousers.

Fahima Hashim, a women's rights activist following Abdalla's case, said sentences were often inconsistent in Sudan because the legal system gave authority to judges to decide punishments. Previous stoning sentences had not been carried out, she said.

Hashim called for the reform of articles in Sudan's criminal code which she said harm women's rights, including one used in Abdalla's case.

As long as this articles remained unchanged, execution by stoning would not be out of the question, she said. "It's a threat. It could happen." (Additional reporting by Khalid Abdelaziz)