In this still image made from video provided by Al Fajer, a Sudanese NGO, Mariam Yahya Ibrahim is seen sitting next to Martin, her 18-month-old son, while holding her baby girl at a prison in Khartoum. File picture: Al Fajer, via AP

Khartoum - Sudanese authorities agreed Thursday to release from police custody a Christian woman who tried to leave the country after her release from death row and was detained with allegedly false documents.

But Meriam Yahia Ibrahim Ishag, 26, who is charged with forgery and providing false information, remained in custody while her lawyers tried to find an acceptable person to guarantee that she would report to judicial authorities as and when required.

“Now the prosecutor decided to let her go home by a guarantee,” one of her lawyers, Mohanad Mustafa, told AFP.

But he said authorities had so far not approved of the candidates they had proposed as possible guarantors.

“We brought many people, but they don't accept,” he said.

Ishag has been held at the police station in Khartoum's Arkawet district since Tuesday after national security agents stopped her and her family from leaving the country with South Sudanese travel papers.

According to her American husband, Daniel Wani, diplomats from the US embassy had escorted the couple and their two children to Khartoum airport, from where they planned to travel to Washington, DC.

Wani said they “want to get out of here as soon as possible” because his wife has received death threats.

But Mustafa said that even if a guarantor secures her release, she will not immediately be travelling to the United States.

“There is a criminal case against her. She cannot leave Sudan,” he said.

South Sudan's embassy says Ishag is entitled to travel with documentation from that country because Wani and her children are South Sudanese.

Khartoum says she should have used a Sudanese passport, and summoned the charges d'affaires of Washington and Juba over the incident.

On May 15, a lower court judge sentenced Ishag to hang for apostasy from Islam, in a case that raised questions of religious freedom and sparked an outcry from Western governments and human rights groups.

Ishag was convicted under Islamic sharia law that has been in force in Sudan since 1983 and outlaws conversions on pain of death.

An appeal court freed her on Monday from the women's prison where she had been detained with her children, one of whom was born in jail after she received the death sentence.

After her release she immediately went into hiding because of the threats to her life.

Christian activists say her “alleged brother” stated that the family would carry out the death sentence if she were acquitted.

US State Department deputy spokeswoman Marie Harf said Washington's charge d'affaires had voiced “our concern that the family should be allowed to depart swiftly from Sudan.”

According to the church, Ishag was born to a Muslim father and an Ethiopian Orthodox Christian mother.

When Ishag was five her father abandoned the family, leaving her to be raised by her mother, according to the Roman Catholic Archdiocese of Khartoum, which said she joined the Catholic church shortly before she married.