Al-Qaeda's operations chief in Pakistan and another top aide are believed to have been killed, US sources say.

Usama al-Kini and his lieutenant, Sheikh Ahmed Salim Swedan, were both killed in recent days, US counter-terrorism officials said.

Unconfirmed reports say the two men were killed by a missile fired by a US drone near the Afghan border.

Kini was believed to be behind last year's deadly attack on the Marriott hotel in Islamabad, they said.

Fifty-five people were killed when a truck packed with explosives rammed the hotel in September 2008.

'Significant'

Both al-Qaeda suspects died in South Waziristan, on Pakistan's border with Afghanistan, an unidentified US counter-terrorism official told Reuters news agency.

"These deaths are a significant near-term degradation of al-Qaeda's leadership," he added.

Kini was involved in the Islamabad Marriott attack, officials say

He gave no details of how the men died.

However, the Washington Post, also citing intelligence sources, said they were killed in a missile strike by a CIA drone aircraft on a building on 1 January.

"They died preparing new acts of terror," the US daily quoted a counter-terrorism official as saying.

The men - both born in Kenya - were on the FBI's most-wanted list over the 1998 bombings of US embassies in Kenya and Tanzania.

Kini was also thought to have been behind an unsuccessful attempt on the life of former Pakistani Prime Minister Benazir Bhutto, who was later killed in a separate attack, US officials said.

The BBC website reported on 1 January that an unmanned CIA aircraft had fired three missiles in the Karikot area of South Waziristan, killing three suspected militants.

The US has launched dozens of similar attacks in recent months, mostly targeting Taleban and al-Qaeda militants in Pakistan's tribal regions.

'Violation'

The lawless tribal areas on Pakistan's border with Afghanistan are considered a sanctuary for the insurgents.

The US says the militants regularly cross over the porous border into Afghanistan where the US troops have been fighting since 2001.

The drone attacks are believed to have been largely on-target, hitting Taleban and al-Qaeda hideouts.

There have been few civilian casualties, officials say.

But Pakistani media and opposition parties term these attacks a violation of Pakistan's sovereignty and territorial integrity and the government has been under immense public pressure to defend its territory against them.