Prime Minister Stephen Harper phoned Afghanistan President Hamid Karzai Wednesday to express his concerns about an Afghan man facing a death penalty for converting from Islam to Christianity.

"President Karzai listened to my concerns and we had a productive and informative exchange of views," Harper said in a written statement.

"Upon the conclusion of the call, he assured me that respect for human and religious rights will be fully upheld in this case."

Meanwhile, The United Church of Canada is suggesting Ottawa use its position in Afghanistan -- with 2,200 troops in the country's south as part of a Canadian-led multinational brigade -- to promote human rights.

These rights include "the rights of Afghans to choose and change religion without fear of losing their lives,'' the letter to Foreign Affairs Minister Peter MacKay said.

"We sent the letter yesterday and as of yet have not had a response," the United Church's Richard Chambers told CTV Newsnet on Wednesday.

Forty-year-old Abdul Rahman has been charged with rejecting Islam under Afghanistan's laws.

He told a judge at a preliminary hearing last week he became a Christian while working for an international aid group helping Afghan refugees in Pakistan some 15 years ago.

He then moved to Germany for about nine years before returning to Kabul in 2002, after the ouster of the Taliban regime.

Rahman was arrested last month after police discovered him in possession of a Bible during questioning over a custody dispute.

Footage of Rahman at last week's hearing shows him leafing through a Bible before saying, "They want to sentence me to death and I accept it, but I am not a deserter and not an infidel. I am a Christian, which means I believe in the Trinity."

If convicted, Rahman could be executed. But there are indications that Rahman's trial could be dropped before it comes to that.

A state prosecutor told The Associated Press that Rahman could be found mentally unfit to stand trial.

"We think he could be mad. He is not a normal person. He doesn't talk like a normal person," prosecutor Sarinwal Zamari told The Associated Press.

Moayuddin Baluch, Karzai's religious adviser, said Rahman is expected to undergo a psychological examination.

"If he is mentally unfit, definitely Islam has no claim to punish him," he said. "He must be forgiven. The case must be dropped."

A western diplomat in Kabul and a human rights advocate -- both of whom spoke to AP on condition of anonymity -- said the government was frantically looking for a way to drop the trial.

The Afghan legal system is based on a mix of civil and Shariah, or Islamic law.

Death is one of the punishments stipulated for apostasy.

Washington, which considers Karzai a key ally, also raised the case with Afghan Foreign Minister Abdullah Abdullah on Tuesday, urging Kabul to uphold religious freedom.

The case is sensitive for Karzai, who depends on foreign troops to battle militants and foreign aid to support the economy. But he also has to take into the consideration of Muslims who support Islamic law.

About 99 per cent of the more than 25 million people in the conservative Islamic country are Muslim.

Two Afghan journalists were sentenced to death for blasphemy three years ago but they fled and sought asylum abroad.

With files from The Associated Press