PESHAWAR, Pakistan - Militants in Pakistan launched rockets at two trucks returning from delivering fuel to Western forces in Afghanistan, killing three people, an official said Saturday -- the latest in a string of attacks targeting a supply route critical to the U.S. fight against the Taliban.

U.S. and NATO forces in landlocked Afghanistan transport up to 75 percent of their supplies through Pakistan, and any serious disruption of that pipeline could hamper operations.

American officials have so far said the uptick in attacks has not affected their ability to operate in Afghanistan so far, but have acknowledged they are looking for ways to improve security along the route and are investigating alternative ways to deliver supplies.

Militants struck the oil tankers Friday as they traveled through the Khyber Pass, said Fazal Mehmood, a government official in the lawless Pakistani tribal area for which the route is named.

The three Pakistanis killed in the attack included a passenger and both drivers, who were taking their vehicles back to Pakistan without the paramilitary escorts that often accompany the convoys on their way to Afghanistan, Mehmood said.

Despite the escorts, convoys also are often attacked in Afghanistan, where U.S. and NATO forces toppled the hard-line Taliban regime in 2001 but have been battling a resurgence by the group.

Militants have also stepped up attacks on terminals holding supplies on the outskirts of Peshawar in Pakistan's North West Frontier Province. Hundreds of vehicles, including Humvees intended for the Afghan army, have been torched in recent weeks, leaving several security guards dead.

Provincial Information Minister Mian Iftikhar Hussain pledged Saturday to continue to provide security for the terminals. But the provincial government has decided to limit the number of containers that can be stored in them to 200, the number that Hussain said travel to Afghanistan each day.

The terminals now hold hundreds of containers, and 3,000 are currently in the southern Pakistani port town of Karachi ready to be transported to Peshawar, said Hussain. Excess containers should be stored in other Pakistani cities, such as Karachi and the capital, Islamabad, he said.

The U.S. has also responded to increased militant activity in Pakistan's semiautonomous tribal areas with occasional missile strikes that have triggered hostility from local residents.

On Thursday, more than 10,000 protesters in Peshawar demanded Pakistan prevent Western use of the supply route to Afghanistan, saying the equipment transported was being used for attacks on Pakistani soil.

Militants have also stepped up attacks elsewhere in Pakistan, including last year's high-profile killing of former Prime Minister Benazir Bhutto in Rawalpindi, just outside the capital of Islamabad.

Pakistani Prime Minister Yousuf Raza Gilani on Saturday announced a new human rights award in honor of Bhutto ahead of the first anniversary of her death on Dec. 27.

The award will be given annually starting next year to two organizations and three individuals who strongly promote human rights as Bhutto did, Gilani said. The government has also announced it will issue a special coin to mark the anniversary.