The Sudanese woman freed from death row has been accused of forging official documents to leave the country, her lawyer has told the BBC.
Meriam Ibrahim was detained on Tuesday, a day after a court released her, annulling the death sentence imposed on her for renouncing the Islamic faith.
Mrs Ibrahim had emergency travel documents issued by South Sudan when she was detained at Khartoum's airport.
Mrs Ibrahim had reportedly planned to travel to the US with her family.
She was sentenced in May to hang for renouncing Islam, sparking an outcry at home and around the world.
She gave birth to a girl while on death row.
Sudan's appeal court overturned the conviction on Monday.
The US says it is working with Sudan to ensure Mrs Ibrahim, 27, is freed.
She was detained along with her husband, Daniel Wani, a US citizen, and their two children.
Mrs Ibrahim's lawyer, Elsherif Ali, told the BBC that Sudan's National Security and Intelligence Authority had lodged the complaint against Mrs Ibrahim, accusing her of forging official documents.
Mrs Ibrahim is being held at a police station in Khartoum, Sudan's capital, he said.
South Sudan's embassy in Khartoum says the travel documents are genuine - her husband is a Christian originally from South Sudan.
Wednesday, June 25, 2014
Ibrahim update: Still detained on phony charges
Unfortunately, reports of Meriam Ibrahim's release have turned out to be false.