Egypt arrested on Wednesday senior al-Qaeda operative, Seif al-Adel, at Cairo airport.
Security officials and state television reported the arrest, but they did not say why the Egyptian militant flew to Cairo.
Adel was reported to have briefly taken over the militant network's leadership after Osama bin Laden's death.
He is also on the FBI's most wanted list with a reward of up to $5 million dollars for his capture.
An airport official said Seif al-Adel, also known as Muhamad Ibrahim Makkawi and Ibrahim Madani, arrived on an Emirates flight from Pakistan with a stop over in Dubai.
Security officials said the militant, a former Egyptian special forces officer, was arrested after presenting a travel document at customs and taken into custody by the National Security apparatus.
They said he was wanted by the powerful security agency but did not detail the accusations against him.
On its website, the US Federal Bureau of Investigation says Adel has been indicted for alleged involvement in the 1998 bombings of US embassies in Kenya and Tanzania.