WASHINGTON ( CNN ) -- Two U.S. military Humvees are missing after suspected Taliban militants attacked a transport convoy carrying equipment destined for U.S. troops in Afghanistan , U.S. military and local officials said Tuesday . U.S. military officials in Afghanistan did not have much detail about Monday 's attack in northwestern Pakistan , but said the supply convoy was carrying at least two Humvees and numerous water tank trailers . As many as 70 armed militants attacked two convoys within 30 minutes at the Khyber Pass , a mountain pass that links Pakistan and Afghanistan , local officials said . The pass is located in Khyber , one of seven semiautonomous tribal agencies along the Afghan border . U.S. military spokesman Maj. John Redfield said he did not know how many transport trucks were stolen , but some reports said militants took as many as 13 . U.S. military officials are working with Pakistani officials to track down the missing trucks . Local officials said it 's believed tribal leaders in the region will hold talks with the militants to try to secure the return of the trucks and their supplies . Khyber Agency officials said some of the trucks seized in one of the attacks were carrying wheat to Afghanistan as part of a United Nations World Food Programme convoy , and one truck contained Humvees destined for the U.S.-led coalition in Afghanistan . Redfield said the convoy had more than 13 transport trucks in it . The Humvees were being carried on a flatbed truck and the water tanks were in container trucks , he explained . No U.S. troops were accompanying the convoy , Redfield said . It was operated by a commercial contract company and was being guarded by Pakistani Frontier Corps troops when the attack occurred Monday , he said . Authorities dispatched two helicopter gunships , which fired on the raiding militants killing one person and wounding another , but could not foil the hijacking , local officials said . The ground route through Khyber Pass is one of many used by U.S.-hired contractors to ferry equipment into the Afghanistan war zone from Pakistan . Over the past year , these ground routes have come under numerous attacks by Taliban and al Qaeda militants , officials said . One raid earlier this year resulted in the hijacking of a truck carrying a U.S. Army helicopter engine . The Pakistani central government has little control in the area , and it is believed to be a haven for militants . The United States uses Pakistan as a supply route because of its major sea port in Karachi . Afghanistan is a land-locked country and the fighting there makes it more difficult to fly in supplies . A suicide bomber struck outside a stadium in northwest Pakistan on Tuesday evening , killing three people and wounding 11 others , the provincial information minister , Mian Iftikhar Hussain , said . The blast occurred outside Qayyum Stadium 's front gate , where a closing ceremony for the Inter-Provincial Games was being held , police said . The ceremony for the sports tournament was just ending when the blast went off , North West Frontier Province police Inspector General Malik Naveed said . Most people had already left the stadium at the time of the attack , he said . In addition to the three dead , the bomber was also killed , police said . Qayyum Stadium is in the heart of Peshawar , the capital of the North West Frontier Province on the country 's border with Afghanistan . The region is rife with Islamic extremists . CNN 's Zein Basravi contributed to this report .
Convoy carrying military supplies , humanitarian aid attacked in Pakistan . Two U.S. military Humvees missing after the suspected Taliban attack . Local tribal leaders to hold talks with militants to try to secure return of supplies . Three killed , 11 wounded in blast outside a stadium holding sports event .