Instead, the arrested man appears to have been mistaken for the al-Qaida leader known as Saif al-Adel, two U.S. officials said, speaking on condition of anonymity to discuss intelligence information that has not been publicly released.
Mohammed Ibrahim Makkawi was arrested on his arrival at Cairo airport from Pakistan via Dubai, Egyptian security and airport officials said.
The FBI includes that name on the list of its 10 most-wanted terrorists as an alias for the senior al-Qaida leader known as Saif al-Adel, 51.
But Makkawi told reporters he was not Saif al-Adel and that he had nothing to do with the terror group since 1989. He said he traveled to Egypt using travel documents issued by the Egyptian Embassy in Islamabad.
The FBI said it was still sorting out details of the case.
"We are aware that an individual has been taken into custody and every effort is being made by the U.S. government to verify the identity of the person in custody," said William Carter, a spokesman at FBI headquarters. He declined to comment further.
Saif al-Adel, an Egyptian, has been indicted by the United States for an alleged role in the Aug. 7, 1998 bombings of U.S. embassies in Tanzania and Kenya that killed 224 people. He is a veteran figure in al-Qaida, believed to have been the head of its military committee.
After the U.S.-led invasion of Afghanistan following the 9/11 attacks, he fled to Iran, where he was reportedly held under house arrest, though it is believed he continued to be active and in recent years he was reportedly allowed to make trips to Pakistan.
Associated Press reporters Pete Yost and Pauline Jelinek contributed to this report.
