Clinton: 'We'll always maintain our right to use force'

US Secretary of State Hillary Clinton implicitly defended Washington's use of drone strikes to kill suspected militants, just days after one of the aircraft killed one of al Qaeda's most powerful figures in Pakistan.

The killing of Libyan-born Abu Yahya al-Libi has fuelled an increasingly fierce debate about the legality and morality of the drones, which have become one of the chief US weapons against al Qaeda but which opponents say stretch the definition of the legitimate use of lethal force.

The strikes by the remotely piloted unmanned craft have also angered Pakistan's government and contributed to unrelenting tension between Washington and Islamabad, which says they kill civilians and violate its sovereignty.

"We will always maintain our right to use force against groups such as al Qaeda that have attacked us and still threaten us with imminent attack," Clinton said in Istanbul.

"In doing so, we will comply with the applicable law, including the laws of war, and go to extraordinary lengths to ensure precision and avoid the loss of innocent life," she told the Global Counterterrorism Forum, a US-and Turkish-chaired group.

Her comments echo those of President Barack Obama's counterterrorism adviser John Brennan, who said in April such targeted drone strikes in other countries were legal.

"As a matter of international law, the United States is in an armed conflict with al Qaeda, the Taliban, and associated forces, in response to the 9/11 attacks, and we may also use force consistent with our inherent right of national self-defense," Brennan said in the speech to a Washington think-tank.

Strikes have focused on the North Waziristan tribal area, near the Afghan border, where Libi was killed early on Monday. US officials also say members of the Haqqani network, one of the most dangerous Afghan insurgent groups, are based there.