Canada has joined the list of countries closely watching a court case in Afghanistan, where under Islamic law a man could be sentenced to death for rejecting Islam.

"Canada will continue to encourage the Afghan government to adhere to its human rights obligations," Foreign Affairs spokeswoman Pamela Greenwell told Reuters Tuesday.

Italy and Germany, two other Western countries with troops stationed in Afghanistan, have also started to express concern over the case amid calls that their troops be pulled out.

Abdul Rahman became a Christian 16 years ago while working in Germany, but he was charged with rejecting Islam only in February, when his family denounced him during a custody battle over his two children.

Rahman, 41, is now in jail in Afghanistan and faces the death penalty unless he agrees to convert back to the faith in which he was raised, said the judge at the Shariah court. (Shariah is the legal code of Islam, based on the Qu'ran.)

"We will invite him again [to renounce Christianity] because the religion of Islam is one of tolerance," trial judge Ansarullah Mawlazezadah told the BBC on Sunday. "We will ask him if he has changed his mind. If so, we will forgive him."

The accused man's mental state will also be taken into account before the court passes sentence, Mawlazezadah added.

Constitution may prevent president's intervention

About 99 per cent of the 28 million citizens of Afghanistan are Muslim, and conservative Muslims dominate the country's judicial system.

The nation's constitution, drafted after the ultra-conservative Taliban government was forced from power four years ago, is based on Shariah law.

That factor makes it hard for liberals such as President Hamid Karzai to intervene in the Rahman case, though he is dependent on financial aid and military support from the West to fight off continuing threats from Taliban militants.

Western nations hint at pulling out troops

On Tuesday, politicians from Italy and German signalled they are unhappy that a man could be put to death merely for being a Christian.

Germany has about 2,700 soldiers stationed in Afghanistan. Italy has 1,775, compared to Canada's 2,200.

A former president of Italy, Francesco Cossiga, has proposed the country pull its troops out unless Rahman's life is spared.

"It is not acceptable that our soldiers should put themselves at risk or even sacrifice their lives for a fundamentalist, illiberal regime," Cossiga wrote in an open letter to Italian Prime Minister Silvio Berlusconi, who faces a re-election battle next month.

Two German cabinet ministers have expressed similar concerns.

On Monday, U.S. State Department spokesman Sean McCormack also addressed the Rahman case.

"Tolerance, freedom of worship, is an important element of any democracy," he said. "These are issues, as Afghan democracy matures, that they are going to have to deal with increasingly."