Sudan summons US ambassador in row over Christian convert

"The airport passport police arrested Abrar after she presented emergency travel documents issued by the South Sudanese embassy and carrying an American visa," Sudan's National Intelligence and Security Services' media department said on Facebook, referring to Ibrahim by her Muslim name.

"The Sudanese authorities considered (the action) a criminal violation, and the Foreign Ministry summoned the American and South Sudanese ambassadors," it added.

Under Sudan's penal code, forging a document is punishable by up to five years in prison.

Ms Ibrahim's lawyer, Mohaned Mostafa, said that she is expected to stay in police custody for 24 hours.

Her case triggered an international outcry and was closely monitored by Washington and London, who last month summoned the Sudanese charge d'affaires to protest against Ibrahim's initial death sentence.

Following her brief release on Monday, Ibrahim was sent to a secret location for her protection after her family reported receiving threats, another one of her lawyers had said.

In Washington, the US State Department offered a different version of events on Tuesday, saying the Sudanese government had told the United States that Ibrahim had been detained for several hours and then released but that she had not been arrested.

"The State Department has been informed by the Sudanese government that the family was temporarily detained at the airport for several hours by the government for questioning over issues related to their travel and I think travel documents. They have not been arrested," State Department spokeswoman Marie Harf told reporters.

"The government has assured us of their safety," Harf added, saying that the US embassy was "highly involved" in working with the family and the government to resolve the matter. "We are engaging directly with Sudanese officials to secure their safe and swift departure from Sudan."

The United States has imposed economic sanctions on Sudan since 1997 over alleged human rights violations. It intensified sanctions in 2006 over Khartoum's actions in its conflict with rebels in the western region of Darfur.

South Sudan, with a majority Christian population, became independent from Sudan after a public vote in 2011 that ended years of civil war between the two states. Islamic laws are applied in Sudan, where most of its people are Sunni Muslims.

The relationship between the two Sudanese neighbors have been relatively calm since South Sudan's secession.