Gunmen attacked three container trucks carrying NATO supplies en route to Afghanistan in Pakistan's troubled northwest on Monday, killing two people, officials said.
The trucks came under fire in the Wazir Dhand 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 three container trucks were on their way to Afghanistan when seven to eight gunmen opened fire at them in Wazir Dhand area, killing two drivers and wounding two others," a senior local administration official, Ali Sher, told AFP.
He said two of the drivers were missing since the incident and it was not clear if they had escaped or if militants had kidnapped them.
Another local administration official also confirmed the incident and said the attackers had fled.
A doctor at the government-run agency headquarters hospital in Jamrud said two dead bodies and two injured were bought to the hospital.
"One of the injured was in critical condition and he has been shifted to Peshawar for further treatment" he said requesting not to be named as he is not authorised to talk to the media.
No group has admitted responsibility but the Taliban have in the past claimed such attacks.
Trucks travelling through Pakistan to supply US-led forces have frequently been attacked during NATO's 13-year intervention in Afghanistan.
The coalition is winding down operations in Afghanistan with its 51,000 combat troops due to pull out by the end of this year.
Late last year the United States suspended shipments of equipment out of Afghanistan through a key Pakistani route for a time.
The move came after the political party of former cricketer Imran Khan began forcibly searching trucks in an effort to halt NATO supplies in protest against US drone strikes in Pakistan.