ISLAMABAD — A mentally ill British man has been sentenced to death in Pakistan after being convicted of blasphemy charges, defense lawyers said Friday.

Mohammed Asghar was arrested in 2010 in Rawalpindi, near Pakistan's capital of Islamabad, for claiming to be the Prophet Muhammad in letters that were later produced at his trial, prosecutor Javed Gul said. But a lawyer that previously defended Asghar said the case was really a property dispute and that Asghar suffers from mental illness.

A judge convicted and sentenced Asghar, who is of Pakistani origin, on Thursday, Gul said.

Asghar returned to Pakistan in 2010 after being treated for paranoid schizophrenia in Edinburgh, the lawyer said.

The defendant later fell into a dispute with a tenant who brought the blasphemy complaint against him to police, the lawyer said.

The doctor treating Asghar in Edinburgh said in a letter dated June 2011 that he suffered from paranoid schizophrenia and believed that the Pakistani and British governments were attempting to control him. The letter was provided to The Associated Press by his lawyer.

The lawyer spoke on condition of anonymity as those involved in blasphemy cases face threats and violence.

Prosecutors disputed that Asghar had mental problems.

The British High Commission in Islamabad said it was aware of Asghar's case and provided assistance to him, though an official there declined to elaborate. Senior British Foreign Office Minister Sayeeda Warsi later said in a statement that authorities "will be raising our concerns in the strongest possible terms with the Pakistani government."

Amnesty International called on the Pakistani government to immediately release Asghar.

"At a time when Pakistan is reeling from a spate of abuses which perpetrators seek to justify as a defense of religious sentiments, reform of the blasphemy laws is more urgent than ever," said Polly Truscott, Amnesty International's Deputy Asia-Pacific Director.

Lawyers said they will appeal Asghar's conviction, and they were worried about his mental condition and physical safety while he is in prison.

Scores of people have been arrested in Pakistan under the country's harsh blasphemy laws, which carry sentences of life in prison or the death penalty, though executions are rarely carried out. Rights groups say the laws often are exploited for personal gain and that members of Pakistan's minority population are disproportionately targeted.

People accused of blasphemy also have been attacked and killed by angry vigilante mobs.

Few leaders in this predominantly Muslim country have shown willingness to tackle the contentious issue, especially after two prominent politicians who criticized the blasphemy law were murdered in recent years. One of the politicians was shot by his own bodyguard, who then attracted adoring crowds.