WASHINGTON - President Barack Obama said yesterday that he has ordered a review of the nation's watchlist system and of its air-safety regulations following a Christmas Day attack on a U.S. airliner. As an al Qaeda group claimed responsibility for the assault, the president said he has directed his national security team to keep up the pressure on those overseas who aim to attack the U.S.

"It's absolutely critical that we learn from this incident and take the necessary measures to prevent future acts of terrorism," Obama said in his first public remarks since the attack on the Detroit-bound airliner.

The group al Qaeda in the Arabian Peninsula claimed responsibility for the attempt to bring down the jet, saying the attack was retaliation for a U.S. operation against the group in Yemen.

"We do not yet have all the answers about this latest attempt, but those who would slaughter innocent men, women and children must know that the United States will . . . do more than simply strengthen our defenses," Obama said in a brief statement from Hawaii where he is vacationing with his family.

"We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists who threaten us, whether they are from Afghanistan or Pakistan, Yemen or Somalia, or anywhere where they are plotting attacks against the U.S. homeland," he said.

Federal authorities met yesterday to reassess the U.S. system of terror watchlists to determine how to avoid the type of lapse that allowed a man with explosives to board the flight in Amsterdam even though he was flagged as a possible terrorist.

In a statement posted on the Internet, al Qaeda in the Arabian Peninsula said 23-year-old Nigerian Umar Farouk Abdulmutallab coordinated with members of the group, an alliance of militants based in Saudi Arabia and Yemen.

Yemeni forces, helped by U.S. intelligence, carried out two airstrikes against al Qaeda operatives in the country this month. The second one was a day before Abdulmutallab attempted to bring down a Northwest Airlines flight as it prepared to land in Detroit.

The terrorist group released what it said was a photo of Abdulmutallab, smiling in a white shirt and white Islamic skullcap, overlaid on a graphic showing a plane taking off. In a second version of the same photo, he is shown with the al Qaeda in the Arabian Peninsula banner in the background.

The claim of responsibility was dated Saturday but posted yesterday on a Web site frequently used by militants to disseminate their messages.

Critics and administration officials have questioned how Abdulmutallab was allowed to board the flight. A senior U.S. intelligence official said authorities were reviewing the procedures that govern the lists, which could include how someone is placed on or moved between the various databases.

"Why wasn't he flagged at a higher screening level?" Homeland Security Secretary Janet Napolitano said on ABC's "Good Morning America." "How did he get an explosive substance on to the plane? All of those are serious questions that we are now looking at."

Passengers have faced stiffer boarding measures since Friday. Authorities warned travelers to expect extra delays returning home from holidays.

The intelligence official said the review will look at what adjustments could be made to avoid the type of gap that allowed Abdulmutallab to fly into Detroit even though Britain had refused to grant him a student visa in May. The official spoke on condition of anonymity to discuss the internal review.

Abdulmutallab is accused of trying to detonate an explosive device hidden on his body as the plane approached Detroit on a flight from Amsterdam last Friday. Law enforcement officials say he tucked below his waist a small bag holding a potentially deadly concoction of liquid and powder explosive materials. The device burst into flames without exploding, according to authorities, and Abdulmutallab was subdued by passengers. The plane landed safely.

His name was one of about 550,000 in the Terrorist Identities Datamart Environment database, known as TIDE, which is maintained by the U.S. National Counterterrorism Center. Inclusion in that database does not trigger mandatory additional airport screening. TIDE is the largest collection of names, and U.S. intelligence and law enforcement as well as trusted allies can nominate "known or suspected terrorists" for this database.

Napolitano conceded yesterday that the aviation security system failed, backtracking from a statement Sunday in which she said the airline security system worked. She said her words had been taken out of context.

"Our system did not work in this instance," she said Monday on NBC's "Today" show. "No one is happy or satisfied with that. An extensive review is under way."

Officials said Abdulmutallab came to the attention of U.S. intelligence last month when his father, Alhaji Umar Mutallab, a prominent Nigerian banker, reported to the American Embassy in Nigeria about his son's increasingly extremist religious views.