A senior al-Qaeda leader in Afghanistan, Abu Laith al-Libi, has been killed, Western counter-terrorism officials have told the BBC.
Libi is thought to have directed recent suicide attacks
News of his death emerged on a website used by Islamist groups. Ekhlaas.org said he had "fallen as a martyr".
Pakistan says it cannot confirm reports that Libi was killed by a US missile strike in Pakistan on Tuesday
Libi is believed to have behind an attack at an Afghan air base last year while the US vice-president was there.
Most analysts say Libi's death would be a blow to al-Qaeda, both symbolically and operationally.
But the BBC's security correspondent Frank Gardner says al-Qaeda has proved itself to be resilient to individual losses and setbacks, and no-one is predicting an immediate decline in attacks in the region.
US Defense Secretary Robert Gates said he did not "have anything definitive" to say about the news, the Associated Press reported.
Libi, 41, has appeared in a number of al-Qaeda videos. In November he appeared alongside al-Qaeda second-in-command Ayman al-Zawahri.
ABU LAITH AL-LIBI
Born: Libya, around 1967
Description: 193cm (6'4") tall, solid build, dark hair and eyes, scars on back
Role: Senior operations commander; al-Qaeda spokesman
He has acted as a spokesman for the group, announcing in 2002 that Osama Bin Laden and Taleban leader Mullah Omar had survived the US invasion of Afghanistan.
Libi was under US intelligence surveillance and most details about him are classified, our correspondent says.
"This individual is in the top half-dozen figures in al-Qaeda... who has a long record of military activity on behalf of al-Qaeda," an unnamed Western official told Reuters news agency.
He is thought to be one of al-Qaeda's most senior field commanders in Afghanistan, and to have directed a number of recent suicide bomb attacks in the east of the country.
The US has linked him the bombing at the US base at Bagram in Afghanistan in February last year that killed 23 people. US Vice-President Dick Cheney was at the base at the time.
Reports say Libi was also active across the border in the Waziristan region of Pakistan.
Unnamed Pakistani intelligence officials say he was killed in a missile attack in North Waziristan on Tuesday.
But Pakistan's main military spokesman, Maj Gen Athar Abbas said it was not possible to confirm Libi's death.
"We cannot negate nor confirm because the moment it happened, they removed the bodies and buried them," Maj Gen Abbas told the AFP news agency.
"So, how would anybody confirm who got killed?"
He did not say who buried the bodies.
Seven Arabs and six Central Asians died in the missile strike that hit a village near Mir Ali, Pakistani intelligence officials said.
One told Reuters: "The missile appeared to have been fired by a drone."
Residents reported having seen a drone aircraft in the region before the attack.
Correspondents say the US has launched a number of strikes at suspected militants in Pakistan - some of them missiles fired by drones.
Pakistan has repeatedly insisted in public that it will not accept foreign military action on its territory.
Two years ago Pakistan complained to the US after a similar strike, reportedly aimed at al-Qaeda number two Zawahri, killed 18 people in a village near the Afghan border.