The Pakistani army said Wednesday it found the wreckage of a suspected U.S. spy plane near the Afghan border, but denied claims that it had been shot down.

The incident comes amid strained ties between Washington and Islamabad over a series of missile strikes from American drones at suspected militants targets on the Pakistan side of the border.

In more signs that the militancy was escalating, a homicide bomber killed an 11-year-old girl and wounded 11 troops in the frontier city of Quetta while security forces killed 20 militants in another border zone.

On Wednesday, a militant group that claimed responsibility for last weekend's Marriott hotel bombing threatened more attacks. The warning came in a cell phone message sent to reporters.

"All those who will facilitate Americans and NATO crusaders ... will keep on receiving the blows," said the message from the group calling itself "Fedayeen al-Islam" or "Islam commandos."

Authorities were not immediately available to comment on the threat.

The Pakistan army statement on Wednesday said security forces had recovered the crashed surveillance aircraft. It said a technical problem appeared to have brought it down and that it was investigating further.

The U.S.-led coalition in Afghanistan said one of its drones, which can be equipped with video surveillance equipment, went down Tuesday in the Afghan province bordering Waziristan. But it said coalition forces retrieved it and that no others were missing. The CIA also operates drones in the region.

Three Pakistani intelligence officials earlier had said troops and tribesmen had shot down the drone late Tuesday near Jalal Khel, a village in Pakistan's South Waziristan region.

Confirmation of Pakistani forces firing on U.S. troops or aircraft could trigger a crisis in relations between the two countries, who are close but uncomfortable allies in the American-led war on terrorism.

Pakistani leaders are condemning stepped-up American operations across the border from Afghanistan — especially a highly unusual raid into South Waziristan by U.S. commandos on Sept. 3.

The government says it is trying to resolve the dispute diplomatically.

However, the army has vowed to defend Pakistan's territory "at all cost," and Tuesday's incident was at least the third this month in which Pakistani troops have reportedly opened fire to counter an incursion.

President Bush did not directly refer to the incursions after he met his Pakistani counterpart, Asif Ali Zardari, for the first time in New York on Tuesday.

"Your words have been very strong about Pakistan's sovereign right and sovereign duty to protect your country, and the United States wants to help," Bush said.

The three Pakistani intelligence officials said the drone was hit after circling for several hours. Wreckage was strewn on the ground, they said, speaking on condition of anonymity because they were not authorized to brief the media.

A senior U.S. official challenged the account. "We're not aware of any drones being down," said the official, who also asked for anonymity because of the diplomatic sensitivity of the issue.

American officials have been pressing Pakistan to take stiffer action against militants in its tribal belt, a wild mountainous region considered a staging ground for attacks in Afghanistan and Pakistan, including Saturday's massive truck bombing of the Marriott Hotel in Islamabad that killed 53 people.

Pakistan insists it is doing what it can and complains that cross-border raids fuel Islamic extremism.

Troops are already locked in grinding campaigns against militants in three regions of the northwest. Hundreds have died and more than 500,000 were forced to flee their homes.

A government official in the Bajur region said Wednesday that security forces backed by helicopter gunships had killed at least 20 more militants in fighting that erupted the previous day near Khar, the main town.

Militant warlords have established virtual mini-states in the tribal belt, levying taxes and enforcing strict Taliban-style social codes and justice.