WASHINGTON - Al-Qaeda in the Arabian Peninsula claimed responsibility yesterday for the Christmas Day attack on a Northwest Airlines jet, saying it was retaliation for a U.S. operation against the group in Yemen. Officials in Yemen said suspect Umar Farouk Abdulmutallab had spent time there until earlier this month.

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

Yemeni forces, helped by U.S. intelligence, carried out two air strikes against al-Qaeda operatives this month - the second one a day before Abdulmutallab allegedly tried to bring down Northwest Flight 253 from Amsterdam as it prepared to land in Detroit.

The group said he used explosives manufactured by al-Qaeda members.

Yemen's Foreign Ministry said Abdulmutallab was in Yemen from early August until early December, after receiving a visa to study Arabic in a school in San'a. Yemen's government said authorities were investigating his activities during his stay there.

He had previously studied at the school, the Foreign Ministry said, indicating it was not his first trip to Yemen.

It said he was granted a Yemeni visa after authorities were reassured that he had "several visas from a number of friendly countries," the statement said. It noted Abdulmutallab had a valid visa to the United States, which he had visited in the past.

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

Abdulmutallab broke off contact with his worried parents a few months ago, apparently trading a world of wealth for the calling of a jihadist. He abruptly told his family he would abandon the life that had taken him from a $25,000-a-year private school in the West African nation of Togo to a degree last year from the illustrious University College London, then on to Dubai.

That message pushed his father to contact state security officials and later the U.S. Embassy in hopes of someone bringing home his missing son, the youngest of 16 children.

"We provided them with all the information required of us to enable them do this," a family statement read yesterday, without elaborating.

Loved ones back home in Nigeria struggled to understand his actions.

"From very early childhood, Farouk, to the best of parental monitoring, had never shown any attitude, conduct or association that would give concern," his family's statement read.

The Washington Post reported last night that it had reviewed 300 online postings that appeared to be by Abdulmutallab, ones that mused openly about love and marriage, his college ambitions, and his inner struggle as a devout Muslim between liberalism and extremism.

A U.S. official told the Post that federal intelligence officials were reviewing the postings but had not independently confirmed their authenticity. Many of the biographical details in the writings match up with facts already known about Abdulmutallab, the Post said.

The University of Wollongong in Dubai said yesterday that Abdulmutallab had attended the school from January through the middle of this year. Raymi van der Spek, vice president of the university, said he took classes for "about seven months" before leaving the Australian public university.

Not yet known is what Abdulmutallab did over the eight days - including his birthday on Dec. 22 - after his ticket to Detroit was bought.

Harold Demuren, head of the Nigerian Civil Aviation Authority, said Abdulmutallab paid cash on Dec. 16 for the $2,831 round-trip ticket from Lagos, Nigeria, to Detroit via Amsterdam. He said the ticket had come from a KLM office in Accra, Ghana.

On Dec. 24, Abdulmutallab reentered Nigeria for one day to board his flight in Lagos, local officials said. He walked through airport security carrying only a shoulder bag, with explosives hidden on his body, they said.

The family's statement said Abdulmutallab's father reached out to Nigerian security forces about two months ago, then followed up with officials at the U.S. Embassy in Abuja, Nigeria's capital, 11/2 months ago.

"We were hopeful that they would find and return him home," the statement read. "It was while we were waiting for the outcome of their investigation that we arose to the shocking news of that day."

A Nigerian police spokesman declined to comment, and officials with Nigeria's State Security Service could not be reached for comment yesterday. A spokesman at the U.S. Embassy in Abuja said he had no information on the father's efforts.

A U.S. official, speaking on condition of anonymity, previously said the embassy had shared the father's fears with liaison staffers from such agencies as the FBI, then passed the information to the State, Justice and Homeland Security Departments.

The family promised to cooperate with Nigerian and U.S. authorities.

"We, along with the whole world, are thankful to almighty God that there were no lives lost in the incident," the statement read. "May God continue to protect us all, amen."