CAIRO: al Qaeda's Yemeni offshoot on Monday confirmed the killing of US-born militant cleric Anwar al-Awlaki late last month and vowed to avenge the prominent propagandist's death.

The 40-year-old al-Awlaki, who died in a September, 30, US drone strike in the mountains of Yemen, was the most prominent al Qaeda figure to be killed since Osama bin Laden's death in a US raid in Pakistan in May.

He had been in the US crosshairs since his killing was approved by President Barack Obama in April 2010 - making him the first American placed on the CIA ''kill or capture'' list.

On Monday, al Qaeda in the Arabian Peninsula said in a statement posted on Islamist extremist websites that al-Awlaki was killed by an American airstrike, along with three other militants, according to the SITE Intelligence Group, which monitors extremist websites. AQAP, which has become the most active al Qaeda branch in recent years, vowed to strike back.

''The blood of the sheik (al-Awlaki) and his brothers will not go in vain; there are heroes behind him who do not sleep under oppression, and they will retaliate soon,'' the group said.

''We and the Americans are at war: we get them and they get us, and the end is for those who are patient - they are the ones who will be victorious.''

The strike that killed al-Awlaki also killed a second American, Samir Khan, who edited al Qaeda's Internet magazine. AQAP said two other militants were also killed.

Al-Awlaki, born in New Mexico to Yemeni parents, was believed to be key in turning al Qaeda's affiliate in Yemen into what American officials have called the most significant and immediate threat to the Untied States.

The branch plotted several failed attacks on US soil - the botched Christmas 2009 attempt to blow up an American airliner heading to Detroit and a foiled 2010 attempt to send mail bombs to Chicago-area synagogues.

Known as an eloquent preacher who spread English-language sermons on the internet calling for ''holy war'' against the United States, al-Awlaki's role was to inspire and - it is believed - even directly recruit militants to carry out attacks.

In its statement Monday, AQAP warned that while the US may have killed al-Awlaki, ''it cannot kill his ideas,'' and that his death ''gives new life and revival to his ideas and style.''

It said that al-Awlaki ''has students who he taught and disciples who benefited from him all over the earth, who will follow his steps and his path.''

US officials believe al-Awlaki became involved in operational planning for AQAP, and Yemeni officials have said al-Awlaki had contacts with Umar Farouk Abdulmutallab, the accused would-be Christmas plane bomber, who was in Yemen in 2009.

In New York, the Pakistani-American man who pleaded guilty to the May 2010 Times Square car bombing attempt told interrogators he was ''inspired'' by al-Awlaki after making contact over the Internet.

Al-Awlaki also exchanged up to 20 emails with US Maj. Nidal Malik Hasan, alleged killer of 13 people in the Nov. 5, 2009, rampage at Fort Hood.

Hasan initiated the contacts, drawn by al-Awlaki's Internet sermons, and approached him for religious advice.