There was no "smoking gun" that could have led US intelligence agencies to thwart an attack by an Al-Qaeda-linked Nigerian aboard a US-bound airliner, a top White House security adviser said yesterday.

US President Barack Obama's counter-terrorism adviser John Brennan said there were several "bits and pieces" of intelligence gathered in the run-up to the botched Christmas Day bombing, and that human or systemic failure lay in not putting together those pieces of a larger puzzle.

"There was no smoking gun. There was no piece of intelligence that said this guy is a terrorist and is going to get on a plane... None whatsoever," Brennan told Fox News as part of a round of talk-show interviews.

"It was a failure to integrate the bits and pieces of information."

The terror scare prompted Obama to order a review of intelligence and security operations to find any breakdowns that allowed Abdulmutallab to get on the plane.

Counterterrorism unit set up in Yemen

Brennan's statements came shortly after the United States and Britain agreed to finance a special counterterrorism unit in Yemen, as Obama for the first time Saturday blamed an Al-Qaeda branch in that Arab country for plotting the attack and training the suspect in how to carry it out.

On Sunday the two countries closed their embassies in Sanaa over security fears.

Brennan said Washington closed its embassy because "there are indications that Al-Qaeda is planning to carry out an attack against (a) target inside of Sanaa, possibly our embassy."

Obama on Saturday accused Al-Qaeda in the Arabian Peninsula (AQAP), a Yemen-based cell of Osama bin Laden's group, of targeting a Northwest jet carrying 290 people as it approached Detroit.

But Brennan indicated that the United States was not opening a new front against Al-Qaeda in Yemen and has no plans to send troops there.

"I wouldn't say we're opening a second front. This is a continuation of an effort that we had underway, as I said, since the beginning of the (Obama) administration," said Brennan.

Obama promised to hold AQAP to account and said US probes were revealing new evidence about the suspected bomber, Umar Farouk Abdulmutallab of Nigeria.

New evidence against suspect

"We know that he traveled to Yemen," Obama said in his weekly video address.

"It appears that he joined an affiliate of Al-Qaeda," and that the group "trained him, equipped him with those explosives and directed him to attack that plane headed for America."

Adulmutallab is suspected of trying to destroy the jet by setting off explosives stitched into his underwear. The detonator failed to set off the explosives, instead lighting a fire which was put out by passengers and crew.

Brennan also accused a radical Yemeni cleric, Anwar al-Awlaqi, of trying to "instigate terrorism" due to his alleged links to both the Christmas plane bomb plot and the shooting that killed 13 people at a US military base in November.

"I think what we are clear about is that Mr Awlaqi was in touch with (alleged Fort Hood shooter Major Nidal) Hasan... and there are indications that he had contact, direct contact, with Abdulmutallab," Brennan said on CNN .

"Mr Awlaqi is a problem. He's clearly a part of Al-Qaeda in (the) Arabian Peninsula. He's not just a cleric. He is in fact trying to instigate terrorism."

Obama was expected back in Washington Monday after a family vacation in Hawaii, on the eve of a key meeting on the attack with chiefs of US spy agencies and government departments with national security responsibilities.

General David Petraeus, the US regional commander, met Yemeni President Ali Abdullah Saleh on Saturday, but few details were made public of the talks, which coincided with reports of American involvement in strikes against extremists there.

Michael Leiter, director of the US National Counterterrorism Center (NCTC), warned on Saturday the Christmas Day attack would not be the last.

"While this attempt ended in failure we know with absolute certainty that Al-Qaeda and those who support its ideology continue to refine their methods to test our defenses and pursue an attack on the homeland," he said.

The NCTC was set up after the September 11 attacks in 2001 exposed a disastrous lack of intelligence-sharing among US spy services, but has been one of several agencies criticized over the Northwest Airlines attack.

- AFP