Pakistani security forces have arrested what they say is a senior al Qaeda operative from Yemen in the southern city of Karachi, the military said on Tuesday.
The army identified the man as Muhammad Ali Qasim Yaqub, alias Abu Sohaib al Makki, and said he had been "working directly under al Qaeda leaders along (the) Pakistan-Afghan border".
It was unclear how senior al Makki actually is. The US Embassy in Islamabad was unfamiliar with his name and he does not appear on any lists under the US Rewards for Justice programme.
"The arrest of al Makki is a major development in unravelling the al Qaeda network operating in the region," the military said in a statement.
It was announced a day after senior visiting US senator John Kerry warned Pakistani leaders that Congress was asking "tough questions" about aid to Islamabad after al Qaeda leader Osama bin Laden was killed on Pakistani soil.
The military did not give details on al Makki's rank in al Qaeda or when he was arrested.
A senior security official in Islamabad said al Makki was between 35 and 40 years old and had been living with his three children and wife "for some time".
"He gave some information about movements of some people," the official said, referring to militants. "We are evaluating that information and planning actions."
Military sources added that al Makki came to Pakistan in 2001 and operated in the border area between Pakistan and Afghanistan.
None of the information from the military could be independently corroborated or confirmed.
"He was hiding in a house right in the middle of the city," a senior security official said.
"The arrest was made after intelligence operations began in various cities after May 2. The intelligence operation is still on."
Pakistan is facing mounting pressure to explain how Saudi-born bin Laden appeared to have spent years in Pakistan about a two-hour drive from intelligence headquarters.
US special forces killed bin Laden in a secret raid on his compound on May 2.
The arrest came a day after gunmen on motorcycles shot dead a Saudi diplomat in Karachi as he drove to work.