ISLAMABAD A suspected U.S. drone strike killed eight militants of German nationality in northwest Pakistan on Monday, Pakistani intelligence officials said.
They died when two missiles from a suspected CIA pilotless aircraft struck a mosque in Mirali in North Waziristan, the officials added.
The attack came a day after the United States and Britain warned of an increased risk of terrorist attacks in Europe. Western security officials said last week they believed a group in northern Pakistan were connected to a plot to stage attacks.
The militants were members of a group called Jihad Islami, the Pakistani intelligence officials said without elaborating. There was no independent verification and militants often dismiss official reports of successful operations against them.
"People were gathering at the mosque for prayers when a missile hit the building," Mohammad Alam, a resident of Mirali, told Reuters by telephone, describing Monday's drone strike.
"The area has been cordoned off by militants and they are not allowing anyone there."
The State Department warned American citizens to exercise caution if traveling in Europe. Britain raised the threat level to "high" from "general" for its citizens traveling to Germany and France.
The immediate trigger for Sunday's travel alerts was intelligence about a plot against European targets reportedly originating with a group of individuals in mountainous northern Pakistan, some of them believed to be European citizens.
One security official in Germany said last week word of the plot had probably originated from the interrogation of a German-Afghan suspect in Afghanistan.
The suspect believed to be behind the intelligence was identified by media as Ahmed Sidiqi, a German of Afghan origin. German media said he came from Hamburg and had been held in the U.S. military prison of Bagram in Afghanistan since July.
German counter-terrorism expert Guido Steinberg told Reuters Sidiqi was a member of a cell of militants from Hamburg that was believed to be a central component of the conspiracy.
Steinberg said the cell left for Pakistan in March 2009 and joined Pakistan-based members of the Islamic Movement of Uzbekistan (IMU), a Central Asian militant organization.
CNN reported the 11-strong group included a German of Syrian descent and a German of Iranian descent while an associate of the plot was a Frenchman of Algerian origin, it said
Sidiqi divulged new, unverified information every day, CNN reported German intelligence sources as saying.
The United States has increased drone aircraft strikes on al Qaeda-linked militants in Pakistan's northwest, with 21 attacks in September alone, the highest number in a single month.
It is as yet unclear, however, how closely these intensified drone strikes are linked to the reported plot in Europe.
NATO helicopters from Afghanistan have also attacked militant targets within Pakistan, drawing anger in Islamabad which has condemned these as violation of sovereignty.
Pakistan blocked one of the supply routes for NATO troops in Afghanistan after a helicopter strike last week killed three Pakistani soldiers in the western Kurram region.
NATO incursions and closure of the route have raised tensions between the United States and Pakistan, whose long relations have are often uneasy.
The CIA has also been trying to eliminate leaders of the Haqqani network, an Afghan Taliban faction operating out of North Waziristan which is one of the most effective forces fighting U.S.-led NATO troops in Afghanistan.
North Waziristan, a forbidding tribal area, is home to a variety of militants fighting the Pakistani government or battling U.S.-led NATO troops in Afghanistan, or both.
Some are foreigners who have taken up the cause of holy war against the West and see North Waziristan as a safe haven or training ground. U.S. officials say drones are valuable weapons which have killed high-profile Taliban and al Qaeda figures in an area in northwest Pakistan described as a global hub for militants.
Pakistan worries the strikes undermine efforts to deal with militancy because civilian casualties inflame public anger and bolster support for the fighters.
Elimination of high-profile targets could not be possible without Pakistani intelligence, however, analysts say.
(Additional reporting by Kamran Haider in ISLAMABAD and William Maclean in LONDON; editing by Myra MacDonald)