Two suspected American missile strike killed 16 alleged militants in a northwest Pakistani tribal region Saturday, two intelligence officials said, a sign the U.S. is unwilling to stop using the unpopular tactic despite heightened tensions between the two countries over recent border incursions by NATO.

The Pakistani Taliban, meanwhile, claimed responsibility for an attack on NATO oil tankers in Pakistan's south, saying they were avenging the killing of three Pakistani border guards by NATO helicopters. In apparent retaliation for the killings, Pakistan has cut off a key U.S. and NATO supply line on its soil.

A surge in U.S. missile strikes in Pakistan along with NATO operations along the border suggests Western forces are cracking down on insurgents who easily move between Afghanistan and Pakistan's porous boundary — something Islamabad has been slow to do despite pleas from Washington. Pakistan's willingness to block the supply line amid public outrage, however, shows the leverage it has over the U.S. and NATO.

The suspected U.S. missiles struck buildings Saturday morning in the Datta Khel village of North Waziristan tribal region, the Pakistani officials said on condition of anonymity because they were not authorized to talk on the record to the media. Datta Khel has been the scene of several such attacks on Taliban and al Qaeda fighters and their local supporters who are accused of targeting NATO and U.S. forces in Afghanistan.

Over the past five weeks, the U.S. has launched at least 22 missile strikes in Pakistani territory, an unprecedented number. Western officials say some of the CIA-controlled, drone-fired strikes have been aimed at disrupting a terror plot against European cities.

U.S. officials rarely discuss the covert program, but have described it in the past as a highly successful tool that has taken out some top militant leaders. Pakistan, while formally opposing the missile strikes, is believed to secretly provide intelligence for them. Polls show deep opposition among Pakistani citizens to the strikes, along with a belief that they kill large numbers of civilians.

Public outrage has also risen over the recent NATO incursions. It hit a peak on Thursday, when two NATO helicopters crossed into Kurram tribal region and killed three Pakistani paramilitary soldiers who fired warning shots at them from a border post.

Pakistanis responded with protests on Friday, and the Taliban attacked 27 NATO oil tankers, setting them abaze.

Angry mobs blamed the U.S. and NATO for Pakistan's problems. One protest banner carried the message, "Who is responsible for the destruction of Pakistan?"

Khurshid Ahmed, a member of the opposition party in Pakistan, demanded that the NATO strikes stop.

"We regard it as an act of war, and we have demanded that Pakistan government must take immediate steps," he said, "both stopping supplies to NATO and, No. 2, if our borders are violated we should strike back."

Pakistani Taliban spokesman Azzam Tariq told The Associated Press that his organization was behind the assault on the tankers, and threatened more attacks — including ones inside the United States.

"We ask the government of Pakistan to cut all the supply routes for NATO, otherwise we will continue targeting NATO's fuel trucks and containers," he told AP via phone. "We condemn the NATO attack on Pakistani forces in Kurram, and this attack proves that Christians and Jews cannot be our friends, and this is what Islam tells us. We will avenge this NATO attack by targeting America. We will carry out attacks inside America."

The Pakistani Taliban is strongest in the northwest, especially in the tribal belt, but it has ties to other militant groups throughout the country. If it played a role in the attack on the NATO oil tankers, it might have relied on foot soldiers from militants with groups based in Sindh.

On Saturday, some 150 trucks were still waiting for Pakistan to reopen the border crossing at Torkham so they could deliver their supplies to Western troops in Afghanistan. But Pakistan has shown no sign it plans to allow the trucks to leave its territory, despite the potential strain a lengthy closure would have on its relationship with the U.S., which provides it with billions in military and other aid.

A second, smaller border crossing in the southwest town of Chaman remains open, but Torkham, in the northwest, is considered much more important.

The Associated Press and Fox News' Jennifer Griffin and Justin Fishel contributed to this report.