Meriam Ibrahim, the Christian woman detained when she tried to travel to the United States after her release from death row in Sudan, was freed again on Thursday and took refuge at the US embassy in Khartoum, her lawyer said. on Thursday

"She is in the US embassy now," Mohanad Mustafa said of Ibrahim. "She and her husband think this is a safe place for them" after receiving death threats.

Ibrahim, 27, had been detained with her husband and two young children at Khartoum airport on Tuesday – over allegations she had forged travel documents – as the family tried to leave the country for the US. But she was discharged from a police station, on the condition she remains in Sudan, after the government came under pressure from foreign diplomats.

In Washington, US state department spokeswoman Marie Harf said Ibrahim and her family were "in a safe location" and Sudan's government "has assured us of the family's continued safety".

Ibrahim, whose father was Muslim but who was raised by her Christian mother, was last month convicted of apostasy and sentenced to hang. She was also sentenced to 100 lashes for adultery after a court ruled her marriage to a Christian man was invalid.

Under Sudan's penal code Muslims are forbidden from changing faith, and Muslim women are not permitted to marry Christian men. Ibrahim insisted she had been brought up as a Christian.

The case prompted outrage, with more than a million people backing Amnesty International's campaign for her release.

On Monday the appeal court annulled her death sentence and freed her, after which she went into hiding because of death threats.

Her husband, Daniel Wani, a United States citizen since 2005, said he hoped the family could start a new life in America. But 24 hours later security service agents apprehended the family, including a baby girl born while Ibrahim was shackled to the floor ofin her cell, claiming that her travel documents were forged. Ibrahim's lawyer Elshareef Mohammed said more than 40 security officers stopped them boarding a plane to Washington.

The US state department said its envoy then met Sudanese foreign ministry officials at their request and told them the family needed to be able "to depart as swiftly as possible from Sudan and that we are happy to help in any way we can".

Wani has claimed that those who triggered the case against his wife, whom he married in 2011, were attempting to muscle in on her business interests, including a hair salon, mini-mart and agricultural land.