* Sudanese woman, initially sentenced to death, living in U.S. embassy
* Lawsuit case could further delay departure for United States
* Case raised international concern
KHARTOUM, July 2 (Reuters) - A Sudanese woman spared a death sentence for converting from Islam to Christianity faces a new lawsuit on Thursday brought by her family to formally establish her as a Muslim, a lawyer said, in a move that could delay her departure for the United States.
Mariam Yahya Ibrahim, 27, was briefly detained last week, a day after an appeals court overturned a death sentence imposed on her for changing her faith and marrying a Christian South Sudanese-American.
The government accused her of attempting to leave the country with falsified travel documents issued from the South Sudanese embassy. Despite lifting the death penalty, Sudan refuses to acknowledge Ibrahim's new identity as a South-Sudanese Christian.
"The Khartoum Religious Court will review on Thursday morning a case asking to prove that Mariam Ibrahim belongs to her (Muslim) father and family," said Abdel Rahman Malek, the lawyer hired by Ibrahim's Muslim family for the case.
Mariam's lawyer Mohaned Mostafa said Ibrahim had not yet been notified with the new case.
The case is expected to further delay Ibrahim's plan to leave Sudan along with her two children and husband, who have all been staying at the U.S. embassy in Khartoum since Ibrahim's release from police custody last Thursday.
Her case has been closely monitored by Washington and London, which last May summoned the Sudanese charge d'affaires to protest against Ibrahim's initial death sentence and urged Sudan to uphold international obligations on freedom of religion and belief.
Under the Islamic laws that Sudan applies, Muslim women are not permitted to marry Christian men. (Reporting by Maaz Alnugomi in Khartoum, Writing by Yasmine Saleh; editing by Ralph Boulton)