WASHINGTON - Yemeni authorities have 12 Americans in custody, and the arrests may be linked to a joint U.S.-Yemeni antiterrorism campaign, State Department spokesman P.J. Crowley said Monday.

Crowley declined to provide details about the case, except to say the department is aware of the arrests and is seeking more information about the people being held.

The revelations come as the U.S. government has been encouraging Yemen to move against al-Qaeda-linked extremists there 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 people from the United States - are training in camps there.

Last Wednesday, Yemeni security officials said authorities had detained several foreigners, including Americans, in an investigation into al-Qaeda's increased activity in the country.

Those arrests 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 Crowley cited were among those reported to have been rounded up last week.

But when 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-Qaeda in the Arabian Peninsula. . . .I'm not going to talk about specifics."

Al-Qaeda's offshoot in Yemen has steadily strengthened since key leaders escaped from a jail in 2006. In 2009 it got another boost by merging with Saudi al-Qaeda extremists to form al-Qaeda in the Arabian Peninsula.

The two Yemeni security officials who said last week that authorities detained foreigners said some were believed to be linked to Umar Farouk Abdulmutallab, the Nigerian suspected of trying to blow up a Detroit-bound jet Dec. 25. U.S. investigators say Abdulmutallab has told them he was trained and instructed in the plot by al-Qaeda 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 officials said.