U.S. missile attacks on suspected militants in Pakistan's northwest near Afghanistan are destabilizing the country and "helping the terrorists," the Muslim nation's Foreign Ministry said Friday.

The comments came as a homicide bomber attacked an anti-insurgent group in a northwest tribal area, killing at least 13 people and wounding more than 50. The Orakzai area tribesmen had gathered to plan the demolition of a militant base.

Al Qaeda and Taliban fighters have established bases throughout Pakistan's semi-autonomous tribal regions, where they are said to plan attacks on U.S. and NATO forces in Afghanistan as well violence in Pakistan.

Washington has pushed Pakistan to eliminate such insurgent sanctuaries.

Pakistan has carried out military offensives against insurgents while also trying to woo various tribes to turn against the extremists. Some pro-government tribes have set up militias to fight insurgents.

But in a sign of U.S. impatience with Pakistani efforts, American forces have stepped up their own crossborder assaults on alleged militant targets.

The U.S. is suspected in at least 11 missile strikes on the Pakistan side of the Afghan border since Aug. 23, killing more than 100 people, most of them alleged militants, according to an Associated Press count based on figures provided by Pakistan intelligence officials.

The United States rarely confirms or denies the attacks, which Pakistan's military and civilian leaders have criticized as violations of the country's sovereignty.

"We want them (the United States) to realize that these attacks are destabilizing the situation, and they are not helping them or Pakistan," Pakistan foreign ministry spokesman Mohammed Sadiq told The AP. "They are helping the terrorists."

The strikes are unpopular among many Pakistanis and used by critics and Muslim conservatives to rally support in their campaign to unseat the country's broadly secular, pro-U.S. government.

The most recent alleged U.S. attack took place late Thursday in North Waziristan and killed at least nine people, between six and eight of them suspected foreign militants, intelligence officials said. They said they were trying to establish the identities of the victims.

The tribal regions also are considered potential hiding places for Al Qaeda leader Usama bin Laden, his deputy Ayman al-Zawahri and other non-Pakistani militants.

Friday's homicide attack occurred in Orakzai, a tribal region near the main northwest city of Peshawar that has been relatively peaceful.

Some 500 people of the Alizai tribe, which has set up a militia to fight insurgents, were gathered when the attacker struck. The tribesmen intended to destroy a major militant base, said Sher Akbar Khan, a government official.

"Initial reports suggest that the homicide bomber rammed an explosive-laden vehicle into the gathering," Khan said, adding that the death toll could rise.

Also Friday, government official Jamil Ahmad accused militants of beheading four pro-government tribal elders Thursday in Bajur tribal region, the scene of the some of the heaviest fighting between Pakistani troops and insurgents.