A suspected U.S. missile strike killed four people in northwestern Pakistan late Thursday, intelligence officials said -- the latest in a spate of attacks close to the Afghan border that have squeezed Al Qaeda and the Taliban.

Such strikes have killed high-ranking militant commanders, including Pakistani Taliban chief Baitullah Mehsud, but have also killed civilians and drawn protest from Pakistani leaders.

Two intelligence officials said the strike took place near the town of Mir Ali in North Waziristan tribal region close to the Afghan border. They spoke on condition of anonymity because they were not authorized to speak to reporters.

Despite Pakistani protests, Washington has shown no sign of abandoning the attacks. Many analysts believe Pakistani security agencies quietly provide intelligence for the strikes.

The border region provides Islamist militants with a safe haven from which they can stage attacks on foreign forces in Afghanistan. The mountainous, lawless area is also a breeding ground for the insurgents who launch near-daily attacks on Pakistan's U.S.-backed government and security forces.

Earlier Thursday, militants ambushed a convoy of prominent anti-Taliban tribal elders in the northwest, spraying their cars with gunfire and killing nine people, police said.

The members of the anti-Taliban citizens' group were traveling from the Machikhel area to meet security officials in Bannu district when their three-vehicle convoy was attacked by insurgents, police officer Mohammad Ghani Khan said.

Pakistani authorities have urged tribal elders to speak out against the Taliban, and in turn the militants have killed scores of local leaders. With government backing, some elders have raised militias, known as lashkars, to battle the insurgents. The militias have been compared to Iraq's Awakening Councils, which helped U.S. forces turn the tide against Al Qaeda there.

The ambush followed a separate attack by militants who killed two members of another anti-Taliban committee Thursday in the Swat Valley to the northeast. The assailants struck as members of the "peace committee" slept in the Sertelegram area, Mayor Mohammad Ibrar Khan said.

In the Swat region, thousands of armed citizens gathered at the Saidu Sharif airport, fearing a possible Taliban comeback following an army offensive that has driven the militants back.

"This is our effort of self-help, and people turned up here with whatever weapon they have from a baton to an assault rifle and pistols. ... We will resist militants and guard our area for a lasting peace," Inamur Rehman, head of the Swat National Council, told The Associated Press.

A leader of the private militia will be chosen in the coming days, Rehman said.

"This is a welcome sign that people have risen to protect themselves and guard against the militants," army Brig. Salman Akber said, adding that security forces would assist the group.