WASHINGTON - President Barack Obama says the U.S. will do everything it can to help Nigeria find nearly 300 teenage girls who have been missing since they were kidnapped from school three weeks ago.

The Islamist extremist group Boko Haram has claimed responsibility for the abductions. The group's leader has threatened to sell the girls.

Obama says the Nigerian government has agreed to accept help from U.S. military and law enforcement officials experienced in these types of situations. He says he can only imagine what the girls' parents are going through.

Obama says the immediate priority is finding the girls.

He says the international community will then have to deal with the threat posed by groups like Boko Haram.

Obama commented Tuesday in an interview with Al Roker of NBC's "Today" program.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

The United States is sending technical experts to aid the Nigerian government's search for nearly 300 teenage girls who were kidnapped from their school in mid-April, the White House said Tuesday. The mass abduction has sparked international outrage and mounting demands for Nigeria do more to free the girls.

"Time is of the essence," said White House spokesman Jay Carney.

President Barack Obama and Secretary of State John Kerry were to discuss the kidnapping Tuesday during one of their regularly scheduled White House meetings.

Kerry repeated the longstanding offer of U.S. assistance during a conversation Tuesday with Nigerian President Goodluck Jonathan.

"The president was very happy to receive this offer and ready to move on it immediately," Kerry told reporters at a State Department news conference with European Union foreign policy chief Catherine Ashton. "We are immediately engaging in order to implement this. We remain deeply concerned about the welfare of these young girls."

The experts, including a team to be assembled by the U.S. Embassy in Abuja, the Nigerian capital, will include U.S. military and law enforcement personnel capable of sharing their skills on intelligence, investigations, hostage negotiating, information sharing and victim assistance, as well as officials with other expertise, Carney said.

The U.S. was not considering sending armed forces, Carney said.

Kerry said the U.S. has been in touch with Nigeria "from day one" of the crisis. But repeated offers of U.S. assistance were ignored until Kerry and Jonathan spoke Tuesday amid growing international concern over the fate of the girls in the three weeks since their April 15 abduction from their school in the country's remote northeast. Kerry said Nigeria had its own strategy for how to proceed.

"I think now the complications that have arisen have convinced everybody that there needs to be a greater effort," Kerry said. "And it will begin immediately. I mean, literally, immediately."

A statement from Jonathan's office said the U.S. offer "includes the deployment of U.S. security personnel and assets to work with their Nigerian counterparts in the search and rescue operation." The statement added that Nigeria's security agencies are working at "full capacity" to find the girls and would appreciate the addition of American "counter-insurgency know-how and expertise."

Nigeria's police have said more than 300 girls were abducted. Of that number, 276 remain in captivity and 53 escaped.

Nigeria's Islamic extremist leader, Abubakar Shekau, has threatened to sell the girls. Shekau also claimed responsibility for the abduction and warned that his group, Boko Haram, will attack more schools and abduct more girls. The group's name means "Western education is sinful."

The State Department on Tuesday warned U.S. citizens against traveling to Nigeria.