Three people died just outside the capital when a building collapsed after it was ravaged by a fire for several hours, a government official said Saturday — a day after militants launched a deadly rocket attack on two trucks returning from delivering fuel to U.S.-led forces in Afghanistan.

The building collapse in Rawalpindi also injured 40, said Haseeb Athar, an official in the garrison town just outside Islamabad. Two people were found dead in the rubble of the four-story shopping plaza and another died after reaching the hospital, he said.

At least six rescue workers who had been trying to put out the fire were still feared trapped by the debris, said Rizwan Naseer, head of a state-run rescue service.

Local television footage showed teams of firefighters spraying water on the twisted wreckage of the building as smoke billowed out in thick, dark clouds.

"It is a complete panic here," said Raja Mohammad Hafeez, a police officer at the scene.

The militant attack, meanwhile, killed three people along a critical and increasingly dangerous supply route, a government official said Saturday.

The militants struck the oil tankers on Friday as they traveled from Afghanistan 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.

Up to 75 percent of the supplies for Western forces in landlocked Afghanistan goes through Pakistan. Al-Qaida and Taliban militants have stepped up attacks on the Khyber supply line in an apparent bid to hamstring U.S. and NATO forces, which toppled the hard-line Taliban regime in Afghanistan in 2001 but have been battling a resurgence by the group.

Hundreds of vehicles, including Humvees intended for the Afghan army, have been torched in recent weeks in terminals on the Pakistani side of the border, leaving several security guards dead. The convoys are often attacked in Afghanistan as well, despite armed escorts.

The attacks have led NATO to scout alternatives for the supply route. The U.S. has also responded to increasing 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 the northwestern city of 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 in other areas of Pakistan, including last year's high-profile killing of former Prime Minister Benazir Bhutto.

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 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.