Western embassies in Sudan expressed "deep concern" on Tuesday over the case of a woman who activists say risks a death sentence for apostasy.
Meriam Yahia Ibrahim Ishag, who says she is Christian, was convicted last Sunday in the Khartoum-area district of Haj Yousef.
"We call upon the government of Sudan to respect the right to freedom of religion, including one's right to change one's faith or beliefs," the embassies of the United States, Canada, the United Kingdom and the Netherlands said in a joint statement.
That right is included in Sudan's 2005 interim constitution as well as in international human rights law, they said.
The court has given Ishag, who is pregnant, until Thursday to recant her faith, Amnesty International says.
A refusal would put her at risk of the death penalty, and she also faces up to 100 lashes for "adultery", the watchdog said in an "urgent action" notice about her case.
The "adultery" charge stems from her marriage to a Christian South Sudanese man, Amnesty said, adding that under Sudan's interpretation of Islamic sharia law a Muslim woman cannot marry a non-Muslim man and any such relationship is regarded as adulterous.
The embassies urged Sudanese legal authorities "to approach Ms Meriam's case with justice and compassion that is in keeping with the values of the Sudanese people".
Sudan's Islamist regime introduced sharia law in 1983 but extreme punishments other than flogging are rare.
Amnesty said Ishag, 27, was raised as an Orthodox Christian, her mother's religion, because her Muslim father was absent.
"It's not only Sudan. In Saudi Arabia, in all the Muslim countries, it is not allowed at all for a Muslim to change his religion," Information Minister Ahmed Bilal Osman told AFP.
Christian Solidarity Worldwide, a British-based group working for religious freedom, said Ishag's case is the latest among "a series of repressive acts" against religious minorities in Sudan.
It said deportations, the confiscation and destruction of church property, and other actions against Christians have increased since December 2012.
But Osman said there is no oppression of Christians.
"We are living together for centuries," he said.
Deportations have only occurred against activists trying to convert people, which is not allowed, the minister said, adding religious buildings constructed without permits will be knocked down.
"Even a mosque, you cannot build a mosque without a licence... If you build it like that, it will be demolished."