Prime Minister Stephen Harper says Afghanistan's president has assured him an Afghan man facing a possible death sentence for converted to Christianity from Islam will not be put to death.

Harper phoned Afghanistan President Hamid Karzai Wednesday to express his concerns about 40-year-old Abdul Rahman who has been charged with rejecting Islam under Afghanistan's laws.

"He (Karzai) certainly conveyed to me that we don't have to worry about any such eventual outcome," Harper told a news conference on Thursday.

In a statement on Wednesday, Harper said Karzai had assured him that respect for human and religious rights would be fully upheld.

German Chancellor Angela Merkel also told reporters she had received assurances from Karzai in a telephone call that Rahman would not be executed.

"I have the impression that he (Karzai) has a firm willingness'' to abide by the human rights requirements, Merkel said going into pre-European Union summit talks."I hope we will be able to resolve this."

Rahman 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.

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

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.

An Afghan judge dealing with the case said on Thursday that the judiciary would not bow to international pressure over the ruling. In the past, death sentences have had to be upheld by the president.

"What it does underscore is the fact that all of Afghanistan's institutions are very fragile," said Harper.

"Its court and judicial system is very nascent and one of the things we're doing there is assisting with the development of governing institutions and I think it underscores why we need to work to make a great deal of progress in that country."

Meanwhile senior Muslim clerics demanded Rahman be put to death, warning that if the government caves in to mounting international pressure and frees him, they will incite people to "pull him into pieces."

"Rejecting Islam is insulting God. We will not allow God to be humiliated. This man must die," said cleric Abdul Raoulf, who is considered a moderate and was jailed three times for opposing the Taliban before the regime was ousted in 2001.

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.

It was not immediately clear when Rahman's trial will resume.

With files from The Associated Press