The White House is to share classified documents with members of the US Congress intelligence committee to prove it has the legal justification to kill al-Qaida-linked American citizens abroad through drone strikes.

The Justice Department move came hours before President Barack Obama's choice for CIA director, John Brennan, seen by many as the architect of the US drone strategy, faced a Senate confirmation hearing.

Brennan was likely to face thorny questions on the CIA drone programme with some senators sceptical about the lawfulness of using the unmanned aircraft to kill American citizens abroad.

Eleven senators, including Democrat Ron Wyden, demanded that Obama offered Congress "any and all legal opinions" outlining the president's authority to use lethal force against Americans.

An unclassified white paper suggested that it would be lawful to use lethal force against al-Qaida-linked US citizens if they posed an imminent threat against Americans and if delaying action created an unacceptably high risk.

The unease of members of Congress over drone strikes has grown louder after three US citizens were killed in a strike in Yemen in 2011. Anwar al-Awlaki and Samir Khan along with Awlaki's 16-year-old son, of Denver, were targeted and killed in two separate drone strikes.

According to US intelligence, Awlaki was senior operational leader of al-Qaida in the Arabian Peninsula (Aqip) involved in plotting attacks against the US.

It was recently revealed how the US has been operating out of a drone base in Saudi Arabia to carry out strikes against Islamist extremists in Yemen over the last two years.

Since the beginning of 2013 at least 24 people have been reportedly killed in at least eight drone strikes on Yemen.

Hundreds of strikes have been reported in Pakistan and Somalia over the last few years although US government officials rarely admit that a drone programme exists.

White House spokesman Jay Carney said Obama was committed to providing more information to Congress - at least with regard to the killing of Americans.

"He thinks that it is legitimate to ask questions about how we prosecute the war against al-Qaida," Carney said.

"These are questions that will be with us long after he is president and long after the people who are in the [Congress] seats that they're in now have left the scene."

John Brennan
US president Barack Obama\'s nominee for CIA Director John Brennan (Reuters)