Obama vows to find plotters

Obama vowed to track down “all who were involved’’ in helping a Nigerian man try to set off explosives aboard a Northwest Airlines flight as the plane approached Detroit, acknowledging the growing conclusion that the act was not that of a lone wolf but of a trained Al Qaeda operative. With more signs pointing to Yemen as the origin of the attack, the White House was weighing how to respond.

The president broke his silence as debate about the episode turned increasingly political. An assertion over the weekend by Janet Napolitano, the homeland security secretary, that the system worked drew strong criticism and forced her to recalibrate it yesterday.

On the international front, a group called Al Qaeda in the Arabian Peninsula, which operates in Yemen and was the target of a recent air strike facilitated by the United States, asserted that it had sponsored the attempted attack in retaliation.

US government officials said they considered the statement, which was posted on a jihadist website, credible. The Yemeni government said yesterday that the suspect in the failed bombing had spent four months in the country before leaving earlier this month.

The claim of responsibility by the Yemeni branch of Al Qaeda could force a shift in the administration’s approach to counterterrorism in that nation. Until now, US authorities considered it important to give Yemen credit for recent strikes against Al Qaeda training camps and leaders, playing down the US role in providing intelligence and equipment.

But a direct attempt by Al Qaeda in the Arabian Peninsula to launch an attack on US soil raises the question of whether the United States should take broader and more clearly visible retaliatory military action. One government official said the topic was likely to come up in meetings of the National Security Council.

Obama, making his first public comments since the episode, said he had ordered his national security team “to keep up the pressure’’ on terrorists and vowed to “use every element of our national power to disrupt, 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 on the US homeland.’’

Although he had been out of sight for three days, he assured Americans he was on top of the situation. “We will not rest until we find all who were involved and hold them accountable,’’ Obama said. “This was a serious reminder of the dangers that we face and the nature of those who threaten our homeland.’’

Meanwhile, Napolitano, who had made the rounds of television talk shows on Sunday, appeared on NBC’s “Today’’ show to try to clarify her statement that the nation’s aviation security system had worked properly.

Napolitano said that her remark had been taken out of context and that the attempted attack in fact represented a failure of the security system. “Our system did not work in this instance,’’ she said. “No one is happy or satisfied with that.’’

In one of her Sunday appearances, Napolitano had said the system worked once the attempted bombing occurred, meaning that the government responded by increasing security and alerting other planes. But she did not qualify her point in another of her appearances, and it seemed incongruous given that the suspect was able to fly to the United States on a valid visa without extra screening, despite having been listed in a terrorism database and buying a one-way ticket with cash and without checking any luggage.

Administration officials said that during a weekend conference call they had resolved to use the Sunday shows to reassure the public, but that the “system worked’’ formulation was not in written talking points.

The visual contrast of a president on vacation while there was anxiety about air travel also drew criticism. Although aides issued statements describing conference calls with counterterrorism advisers, pictures of passengers enduring tougher airport screening were juxtaposed with the image of a president picnicking at the beach and playing basketball, tennis, and golf.

Obama’s remarks coincided with fresh evidence linking Umar Farouk Abdulmutallab, the 23-year-old Nigerian charged in the attempted attack, to Al Qaeda. The statement by Al Qaeda on the Arabian Peninsula, accompanied by a photograph of Abdulmutallab, called him a hero who had “penetrated all modern and sophisticated technology and devices and security barriers in airports of the world’’ and “reached his target.’’

The statement said “mujahedeen brothers in the manufacturing department’’ had supplied the explosives and while a “technical error’’ led to an “incomplete detonation,’’ the group vowed to “continue on the same path.’’

Yemeni officials said immigration records showed Abdulmutallab was in their country from early August until early December. The Yemeni embassy said that Abdulmutallab had previously studied Arabic in Yemen and applied to return this year to study.

Because he had a valid US visa and “there was nothing suspicious about his intention to visit Yemen,’’ he was admitted, the statement said, adding that Yemeni authorities were working to “identify any other individuals who may be linked to him.’’

More details emerged about contacts between Abdulmutallab’s father and the US Embassy in Nigeria. In October, presumably while in Yemen, Abdulmutallab spoke by telephone with his father, Alhaji Umaru Mutallab, a retired banker. His father was so alarmed by his son’s radical talk that he contacted Nigerian officials, who advised him to contact the US Embassy.

Mutallab visited the embassy on Nov. 19 and told officials his son had been radicalized, was missing, and might be in Yemen, said a State Department spokesman, P.J. Crowley. Crowley said Mutallab did not say he believed his son planned to attack Americans, but expressed general concern about his radical views.

The information was taken seriously, Crowley said, but was judged insufficient to warrant revoking Abdulmutallab’s visa, although his file was flagged for investigation if he reapplied. Embassy officials representing several security agencies discussed the information Nov. 20 and sent a cable to Washington. His name was added to a database of 550,000 names with suspicion of terrorist ties, but did not go onto the 4,000-person no-fly list.

Correction: A New York Times story about the attempted bombing of a US airliner on Tuesday's Page One incorrectly characterized the plane ticket used by the suspect. It was a round-trip ticket, and while it was purchased with cash, it was not confirmed that the suspect, Umar Farouk Abdulmutallab, bought the ticket himself.