US President Barack Obama on Tuesday blamed 'human and systemic failures' for allowing a botched Christmas Day attack aboard a Detroit-bound airliner and a US official said the incident was linked to Al Qaeda.

Interrupting a vacation in Hawaii for the second straight day to address the US public, Obama listed several mistakes that allowed a 23-year-old Islamic militant from Nigeria to smuggle explosives onto a plane to the US.

'What is apparent was that there was a mix of human and systemic failures that contributed to this potential catastrophic breach of security,' Obama told reporters.

'There were bits of information available within the intelligence community that could have and should have been pieced together,' he said.

Obama, a Democrat, is under pressure from opposition Republicans who fault the administration for not preventing such an attack and the president for keeping silent about it for three days.

Umar Farouk Abdulmutallab, the suspect who claims to have been trained by al Qaeda in Yemen, is accused of trying to ignite explosives sewn inside his underwear on Northwest Flight 253 from Amsterdam as it approached Detroit. He was subdued by passengers and crew.

An administration official, while declining to confirm that al Qaeda planned the attack, said the White House's latest information showed the Islamic militant group was involved.

The official added that if the information had been better correlated, the attack could have been disrupted.

Meanwhile CNN, citing two unidentified American officials, reported US and Yemeni intelligence agencies were looking at fresh targets for a possible retaliation strike in Yemen.

Yemen has been a longstanding base of support for al Qaeda. Militants bombed the Navy warship USS Cole in the Yemeni port of Aden in 2000, killing 17 US sailors, and Yemenis were one of the largest groups to train in al Qaeda's camps in Afghanistan before Sept. 11, 2001, attacks.

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Obama said he asked to have preliminary findings by Thursday on reviews he ordered after the incident on the way the United States places people on a 'terrorist watch list' and on US air travel screening procedures.

'A systemic failure has occurred. And I consider that totally unacceptable,' the president said.

Abdulmutallab's father had warned US officials weeks ago that his son had adopted extremist views. A CIA spokesman said the father came to the US Embassy in Nigeria and sought help in finding him.

The CIA said it worked with the embassy to add Abdulmutallab and his possible Yemeni contacts to the US terrorism database and forwarded biographical information about him to the National Counterterrorism Center.

The CIA defended its handling of the information, saying the center was set up 'to connect the dots on terrorism.' Obama, without identifying agencies, indicated that connection had not occurred.

'It now appears that weeks ago this information was passed to a component of our intelligence community but was not effectively distributed so as to get the suspect's name on a no-fly list,' he said at a military base near his house.

The failed attack, the most serious such incident in the US since Obama took office in January, has put the president on the defensive over domestic security. It has caused communication missteps by his staff and drawn attention away from his top legislative priority, healthcare reform.

It has also opened the floodgates to Republicans who, facing congressional elections next year, are keen to paint Obama and his Democratic Party as weak on national security.

'The president has been downplaying the threat of terrorism since he took office,' said Senator Jim DeMint.

Obama has ordered preliminary recommendations from the reviews to be ready by Thursday, along with a plan for strengthening aviation screening technology and procedures.

Technology may be part of the solution. Abdulmutallab smuggled the explosives in his underpants through checkpoints in Lagos and Amsterdam and hyper-sensitive body scanners might have prevented this from happening.

But the machines are expensive and also intrusive, exposing an image of the naked body on a security viewing screen.

Beefed up airport security affected the stock markets on Tuesday, with the shares of Air Canada and WestJet Airlines, Canada's two biggest airlines, declining after they warned US-bound travelers to expect more flight delays and cancellations.

A wing of al Qaeda based in Yemen said it was behind the failed bombing to avenge U.S. attacks on the group, according to a web statement.

The Yemeni government, which is fighting Shi'ite rebels in the north and faces separatist sentiment in the south, said the country could be home to up to 300 al Qaeda militants, some of whom may be planning attacks on the West.-Reuters