Gunmen on Thursday opened fire on NATO supply trucks passing through northwest Pakistan near the Afghan border, killing two drivers, local officials said.

The first driver was killed in the Jamrud area of Khyber, one of seven districts that make up Pakistan's semi-autonomous tribal belt where Taliban and Islamist militants are active.

"Two gunmen on a motorcycle fired at a NATO truck and killed its driver," local official Asmatullah Wazir told AFP.

In a separate attack, gunmen opened fire on another NATO supply truck in a suburb of Peshawar, killing its driver, senior police official Muhammad Faysal Murad told AFP.

"The truck was empty and had returned from Afghanistan after delivering supplies," Murad said.

There was no immediate claim of responsibility for the killings.

Pakistan is a key transit route for the NATO mission in landlocked Afghanistan, from where it is driven to the border from the Arabian Sea port of Karachi.

Incoming prime minister Nawaz Sharif, who claimed victory in last week's general election, has promised Pakistan's "full support" as the United States withdraws most of its combat troops from Afghanistan by the end of next year.

From November 2011 to July 2012, Pakistan shut its Afghan border to overland NATO traffic after botched US air raids that killed 24 Pakistani troops.

Pakistan and the United States have signed a deal allowing NATO convoys to travel into Afghanistan until the end of 2015.