Gunmen attacked four vehicles carrying NATO supplies for Afghanistan in Pakistan's troubled northwest on Tuesday, killing two people, officials said.

The vehicles came under fire in the Jamrud area of Khyber, one of seven districts that make up Pakistan's semi-autonomous tribal belt, as they were on their way to Afghanistan.

Pakistan is a major transit supply route for the NATO mission in landlocked Afghanistan.

"The four containers were on their way to Afghanistan when four gunmen riding two motorbikes opened fire at them in Jamrud, killing two helpers and wounding one driver and one helper," a senior local administration official, Jehangir Azam Wazir, told AFP.

He said one of the helpers died on the spot while the second one succumbed to his injuries in hospital.

Another local administration official confirmed the incident and said the attackers had fled.

No group has admitted responsibility but the Taliban have in the past claimed such attacks to disrupt supplies for the US-led international troops fighting in Afghanistan.

The Pakistani Taliban Saturday declared a month-long ceasefire to encourage the resumption of peace talks with the government in Islamabad.

Taliban and Al-Qaeda-linked militants frequently launch attacks across northwest Pakistan and the lawless tribal belt, which Washington has branded the most dangerous place in the world.

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.