HONOLULU: President Barack Obama on Monday vowed to use "every element of our national power" to keep Americans safe and said the failed Christmas Day plot to blow up a Detroit-bound airliner was "a serious reminder" of the need to continually adapt security measures against changing terrorist threats.

U.S. President Barack Obama makes a statement on health care and climate change at the White House in Washington December 19, 2009. Obama on Monday vowed to track down those behind an attempt to bring down a U.S. passenger airline on Christmas Day as he announced stepped-up measures to ensure U.S. flight safety.[Agencies]

But even as Obama spoke, word came that a State Department warning had failed to trigger an effort to revoke the alleged attacker's visa. And officials in Yemen confirmed that the would-be bomber had been living in that country, where terrorist elements quickly sought to take credit for his actions.

The incident prompted stiffer airport boarding measures and authorities warned holiday travelers to expect extra delays as they return home this week and beyond.

Calling Abdulmutallab's action an "attempted act of terrorism" Obama vowed to "do everything that we can to keep America safe" and declared: "The United States will more than simply strengthen our defenses. We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists who threaten us."

Members of Congress, meanwhile, questioned how a man flagged as a possible terrorist managed to board a commercial flight into the United States carrying powerful explosives and nearly bring down the jetliner. Sen. Joe Lieberman, I-Conn., said Monday that the Senate Homeland Security and Governmental Affairs Committee that he chairs would hold hearings in January.

Meanwhile, al-Qaida in the Arabian Peninsula claimed responsibility for the thwarted attack as retaliation for a US operation against the group in Yemen. Yemeni forces, helped by US intelligence, carried out two airstrikes against al-Qaida operatives this month in the lawless country that is fast becoming a key front in the war on terror. The second one was a day before 23-year-old Nigerian Umar Farouk Abdulmutallab attempted to bring down a Northwest Airlines flight as it prepared to land in Detroit.

Yemen has long been an al-Qaida stomping ground. But officials fear that deepening instability in the Middle Eastern nation may be giving new opportunity for the terror group to establish a base to train and plan for attacks on the West.

A statement posted on the Internet by al-Qaida in the Arabian Peninsula said Abdulmutallab coordinated with members of the group and used explosives manufactured by al-Qaida members.

Solving one mystery of Abdulmutallab's pre-Detroit path, the Yemeni Foreign Ministry said Monday that he was in Yemen from August until early December. He had received a visa to study Arabic in a school in San'a. Citing immigration authorities, the statement said Abdulmutallab had previously studied at the school, indicating it was not his first trip to Yemen.

Obama, on vacation in his birthplace of Hawaii, acknowledged the attack showed the need to increase the United States' defenses. He detailed the pair of reviews that he has ordered to determine whether changes are needed in either the watchlist system or airport screening procedures.

"This was a serious reminder of the dangers that we face," he said. "It's absolutely critical that we learn from this incident."

Obama's remarks Monday were the first heard from him on the Christmas Day scare three days earlier.

Officials said that was deliberate — an effort by the White House to balance the need for the president to show concern but also to not unduly elevate a botched incident and thereby encourage other would-be attackers.

Back in Washington, federal officials met to review their layered system of watchlists and other procedures to examine how to avoid the type of lapses that led to the attack.

Abdulmutallab's family in Nigeria released a statement that that his father had reached out to Nigerian security agencies two months ago. The statement says the father then approached foreign security agencies for "their assistance to find and return him home."

US officials say that is how Abdulmutallab came to the attention of American intelligence, just last month, when the father, prominent Nigerian banker Alhaji Umar Mutallab, reported his concerns to the American Embassy in Abuja. A senior US official said the father was worried that his son was in Yemen and "had fallen under the influence of religious extremists." The father did not mention any specific threat.

These concerns landed him among the about 550,000 names in the Terrorist Identities Datamart Environment database, known as TIDE, which is maintained by the US National Counterterrorism Center. Other, smaller lists trigger additional airport screening or other restrictions, but intelligence officials said there wasn't enough information to move him into those categories.

Another apparent lapse concerns Abdulmutallab's visa.

Britain had refused to grant him a student visa in May, but there was no apparent effort to revoke his US tourist visa, issued in June 2008 and good for multiple entries over two years.

The embassy visit by Abdulmatallab's father triggered a Nov. 20 State Department cable from Lagos to all US diplomatic missions and department headquarters in Washington. It was also shared with the interagency National Counter Terrorism Center, said State Department spokesman Ian Kelly.

The NCTC, which has responsibility if any visas are to be pulled over terrorism concerns, then reviewed the information and found it was "insufficient to determine whether his visa should be revoked," Kelly said.

Michael Chertoff, who was homeland security secretary in the Bush administration, questioned why Abdulmutallab's visa wasn't revoked. It's a "serious indicator" when a parent goes to authorities to discuss concerns about his child and it "certainly would cause me to ask questions," said Chertoff in an interview.

Homeland Security Secretary Janet Napolitano conceded Monday that the aviation security system failed, backtracking from a statement Sunday in which she said it worked.

Rep. Pete Hoekstra, R-Mich., joined the GOP critics of that statement. "They just don't get it," said Hoekstra, the top Republican on the House Intelligence Committee. "The system didn't 'work' here." Hoekstra, who is running to become his state's governor, included his criticism in a campaign e-mail that asked supporters for donations.

The White House said Obama's low-key response was carefully calibrated.

The plane had been on the ground in Detroit for two hours on Friday before officials first informed Obama. Advisers said they wanted to make sure they had complete and accurate information before going to the president but, even so, Obama's first briefing with national security and homeland security advisers lasted less than 15 minutes. Obama's motorcade was rolling toward the gym minutes afterward.

Two days later, when another flight from Amsterdam to Detroit came under suspicion, it was about 90 minutes after it landed before Obama was informed of what had been a false alarm.

Throughout the weekend, Obama has mixed vacation activities with crisis monitoring. He played golf on Saturday with friends and was playing basketball with aides when that second flight landed in Detroit on Sunday. He went from there to a beach and a gourmet restaurant dinner in the evening.

On Monday, he did not address the public until after a workout and a tennis game with his wife — and went golfing immediately afterward.