British Christians and Muslims have called for "compassion" in the case of Sudanese Christian mother Meriam Yehya Ibrahim.

The pregnant 27-year-old has been sentenced to death for apostasy in Sudan and is behind bars with her 20-month-old son.

Her execution has been upheld by the court in Khartoum after she refused to recant her Christian faith but will not be carried out until her second child, due next month, is two-years-old.

Co-chairs of the Christian Muslim Forum, Shaykh Ibrahim Mogra and Bishop Paul Hendricks, said the sentence should be dropped out of compassion. 

They said in a statement that it was "vital" people are able to enjoy freedom of conscience and follow their own conscience.

"Our religions tell us that human interactions should be shaped by compassion and humanity, not by death sentences," they said.

"Christians and Muslims should be able to coexist alongside each other, we emphasise that force and compulsion are not characteristics of either faith."

The Archbishop of Canterbury and Patron of the Christian Muslim Forum, the Most Reverend Justin Welby, said he "wholeheartedly" endorsed the call, saying the statement "deserves to be widely shared".

The UK and US governments, and the UN, have all condemned the sentence, while Sudan has brushed off the criticism. 

Britain's Minister for Africa, Mark Simmonds, has condemned the sentence and called upon Sudan to respect religious freedom.

"I am truly appalled that a Sudanese court has sentenced Meriam Yahia Ibrahim Ishag to death for apostasy," he said in a statement.

"This barbaric sentence highlights the stark divide between the practices of the Sudanese courts and the country's international human rights obligations.

"I urge the Government of Sudan to respect the right to freedom of religion or belief, including one's right to follow the religion or belief of their choice, a right which is enshrined in international human rights law as well as in Sudan's own 2005 Interim Constitution.

"The UK opposes the use of the death penalty in all circumstances and urges the Government of Sudan to join what is a clear global trend to abolition."

In a statement, the Sudan embassy in the US said the Sudanese government had been "mistakenly accused" of violating Ibrahim's rights.

"This case remains a legal issue and not a religious or political one," it said. 

"It is unwise and dangerous to politicise the issue at hand to spur religious tension between the two peaceful faiths with similar foundations."

Ibrahim's husband, Daniel Wani, has vowed to fight the sentence, which includes 100 lashes for adultery, and lawyers have lodged an appeal. 

Her case has been picked up by Amnesty International which is spearheading a campaign for her release and says that over 620,000 actions have been taken calling upon the Sudanese government to overturn the sentence.