A senior al-Qaeda leader in Pakistan, Abu Hafs al-Shahri, has been killed, say senior US officials.
There has been no independent confirmation of the death, which officials said happened in the Waziristan tribal region.
The US frequently carries out drone air strikes against suspected militants hiding out in the volatile area.
Three weeks ago, the US said it had killed al-Qaeda's suspected chief of operations, Atiyah Abd al-Rahman.
The media are denied access to the area, making it difficult to confirm such claims.
The US said Shahri has been killed earlier this week and that his death "removes a key threat inside Pakistan".
He had played a "key operational and administrative role" in al-Qaeda and had worked closely with the Taliban to carry out attacks in Pakistan, said officials.
The death would "further degrade al-Qaeda's ability to recover" from the death of Abd al-Rahman, they said, as Shahri had been considered a contender to take on some of the dead leader's duties.
A US official told the BBC that the death represents a blow to the core of al-Qaeda in the country.
The US does not routinely confirm drone operations and there was no immediate comment from Pakistani officials.
However, correspondents says that Arab newspapers had already reported on the killing of Shahri, saying his relatives in Saudi Arabia had received an anonymous phone call to inform them he had been killed in a US drone strike.
The BBC's Ilyas Khan, in Islamabad, says a drone strike near Mir Ali in Waziristan last Sunday is known to have killed a key leader of the Haqqani network.
North Waziristan remains the headquarters of the Haqqani leadership and the main militant bastion in the semi-autonomous tribal belt.
Reports since have suggested that an Arab man whose identify was not clear was also killed, says our correspondent.
The Haqqani network has been blamed for several large attacks in Afghanistan, including a 20-hour gunfight in central Kabul earlier this week.
Abd al-Rahman was killed in Waziristan on 22 August, a US official said. He had reportedly been number two on a list of the five top militants in Afghanistan and Pakistan whom Washington and Islamabad most wanted to capture or kill.
He was considered a close confidant of Osama Bin Laden, who was killed by US special forces in a raid in northern Pakistan in May, and was heavily relied on by the group's new leader, Ayman al-Zawahiri.
News of Shahri's death comes at a time of further tension between the US and Pakistan.
On Wednesday, the US Defence Secretary Leon Panetta said the US would retaliate against insurgents on Pakistani soil. Pakistani officials said his comments were out of line.