The US conducted three drone strikes in as many days killing 27 people. The latest in this series was on Monday when 15 people were killed in North Waziristan. Sources now say that senior al Qaeda leader Abu Yahya al-Libi was the target in one of the three strikes.
US government sources said they were unable to confirm whether Libi had been killed. But officials said he was regarded as a very senior aide to al Qaeda leader Ayman al Zawahiri, and that if he his killed, it would deal a major blow to what remains of the central al Qaeda network founded by the late Osama bin Laden.
Libi is a Libyan militant who has appeared in al Qaeda promotional video messages and once escaped from a US-run prison in Afghanistan.
According to reports from the region, which American government sources did not contest, US-operated drones launched three attacks in tribal areas along Pakistan's border with Afghanistan between Saturday and Monday.
Reports from Pakistan said nearly 30 people were killed during the sequence of strikes, including four suspected militants on Saturday, ten suspected militants on Sunday, and 15 people in the strike in which Libi was targeted.
There have been eight US drone strikes on targets in Pakistan since President Barack Obama and Pakistani President Asif Ali Zardari attended a NATO summit in Chicago on May 21.
In a diplomatic rebuff reflecting the troubled state of relations between the two countries, Obama declined to meet separately with Zardari, but spoke to him for a few minutes during a picture-taking session.
Drones continue despite criticism
Pakistani officials stepped up public criticism of US drone attacks. Pakistan's foreign ministry said it "strongly condemns" American drone strikes which it described as "illegal attacks" on Pakistani sovereignty.
The Pakistan government says the CIA drone campaign fuels anti-American sentiment in the country, and is counterproductive because of collateral damage.
US officials, however, say such strikes by the remotely piloted aircraft are highly effective against militants and are an important weapon in this kind of war.
"The United States is conducting, and will continue to conduct, the counter-terrorism operations it needs to protect the US and its interests," said one American official.
"The real threats to Pakistan's sovereignty are the al Qaeda terrorists who are living within their borders and planning attacks on Pakistan, their neighbours, and the West."
US officials repeatedly have expressed Washington's concerns about Pakistani authorities' reluctance to crack down on militants operating on their territory. They have also complained about alleged collaboration or support provided to militants by Pakistan's principal intelligence agency, the Inter Services Intelligence directorate (ISI).
Last week a US Congressman wrote to Obama asking the US president to explain under what legal justification were drones being operated and that attacks on targets in Pakistan were an indication of an undeclared war on US' chief War on Terror ally.