WASHINGTON (AP) — Yemeni authorities have 12 Americans in custody, and the arrests may be linked to a joint U.S.-Yemeni anti-terror campaign, a State Department spokesman said Monday.

The spokesman, P.J. Crowley, declined to provide details about the case, except to say the State Department is aware of the arrests and is seeking more information about the individuals being held.

The revelations come as the U.S. government continues to encourage Yemen to move against al-Qaida-linked militants in the country who officials fear may be involved in plots to attack America or other Western interests. U.S. officials worry that Yemen is becoming the next significant terrorist staging ground and say insurgents — including some individuals from the U.S. — are training in camps in Yemen's vast undergoverned spaces.

Last Wednesday, Yemeni security officials said authorities had detained several foreigners, including Americans, Britons and an Australian woman, in connection with an investigation into al-Qaida's increased activity in the country.

The arrests reported last week were made after foreign intelligence agencies provided lists of names of people they wanted to have detained or put under surveillance, according to two Yemeni security officials, who spoke on condition of anonymity because they are not permitted to brief journalists.

It was not immediately clear whether the 12 Americans cited by Crowley were among those reported to have been rounded up last week, but Crowley suggested there may be an anti-terrorism connection.

Asked whether he could confirm a report that the Americans had been picked up in Yemen at the request of the U.S. government, Crowley replied, "We have great cooperation with the government of Yemen. Together, we are doing our best to help Yemen reduce the threat posed by al-Qaida in the Arabian Peninsula. That's a threat to Yemen. It's a threat to the United States. But beyond that, I'm not going to talk about specifics."

Al-Qaida's offshoot in Yemen has steadily increased in strength since key leaders escaped from a Yemeni jail in 2006. In January 2009 it got another boost by merging with Saudi al-Qaida militants to form al-Qaida in the Arabian Peninsula.

The two Yemeni security officials who said last week that authorities had detained several foreigners on suspicion of connections to al-Qaida said some of them are believed to be linked to the Nigerian man suspected of attempting to blow up a Detroit-bound airliner in December. U.S. investigators say the Nigerian, Umar Farouk Abdulmutallab, has told them he was trained and instructed in the plot by al-Qaida in Yemen.

Some of the detainees are also thought to be connected to radical American-Yemeni cleric Anwar al-Awlaki, who is believed to have inspired attacks on the U.S. and is hiding in Yemen, the Yemeni security officials said.

The Defense Department in recent months approved spending $155 million to help Yemen in its fight, including the purchase of four helicopters to support counterterrorism operations there. The money also includes $34.5 million to train and equip the Yemeni special forces and another $38 million for aircraft to allow those forces quicker access to hotspots in the country.