Gunmen in southwestern Pakistan torched eight NATO oil tankers and shot dead a driver Wednesday, police said, in the latest strike against supply convoys heading for Afghanistan since Pakistan shut a key border crossing to international forces last week. The attack occurred in a parking area of a roadside hotel on the outskirts of Quetta, the capital of Baluchistan province. At least eight trucks were on fire, and around a dozen others were parked nearby, senior police official Hamid Shakil said. Firefighters were trying to douse the flames. The attacks highlight the precariousness of NATO's efforts to supply troops in Afghanistan. While Pakistan is the fastest and cheapest way to get materials to forces, it is also one of the most dangerous, and fragile ties with Islamabad threw another wrench in the works when Pakistan closed the Torkham crossing in the northwest in apparent reaction to alleged NATO helicopter strikes on its territory. The U.S. has had trouble with other routes in the past: Uzbekistan evicted U.S. troops from a base that was used to ferry supplies into Afghanistan, and, last year, Kyrgyzstan threatened to do the same. At that time, Washington noted that the possibility of losing the Kyrgyz base was not terribly worrying since Pakistan was its main route anyway. The Kyrgyz government has since backed down. The tankers hit Wednesday were believed headed for a smaller Pakistani border crossing at Chaman that remains open. It was unclear who was behind the attack, but the Pakistani Taliban have claimed responsibility for similar assaults on NATO supplies, including one before dawn Monday that killed four people. The militants claimed it was revenge for the NATO helicopter incursions. Counting Wednesday, there have been at least six attacks on the supply convoys since the Torkham closure -- four of them that were heading to that crossing and two on their way to Chaman in the southwest. The events of the last week have exposed the often-strained nature of the alliance between Pakistan and the United States. But analysts doubt it will reach a breaking point because each side is so reliant on the other. In addition to safe passage for NATO supplies, the U.S. needs Pakistan to help target Taliban and al-Qaida militants who stage cross-border attacks against foreign troops in Afghanistan. In return, Pakistan receives billions of dollars in military and civilian assistance that help keep its economy afloat. Both American and Pakistani officials have predicted the Torkham border crossing will reopen within a few days. NATO's Secretary-General Anders Fogh Rasmussen tried to reduce the tension between the two sides Monday by apologizing for last week's helicopter attack that killed Pakistani troops, saying the casualties were 'unintended' and that a joint investigation was under way. But even if the border is reopened, underlying tensions will remain in the U.S.-Pakistan relationship, especially over Pakistan's unwillingness to go after Afghan Taliban militants on its territory with whom it has strong historical ties and who generally focus their attacks on Western troops, not Pakistani targets. The U.S. has responded by dramatically increasing the number of CIA drone strikes in Pakistan's tribal belt, carrying out 21 such attacks in September -- nearly double the previous monthly record. The U.S. has also stepped up military operations along the Afghan border, but officials in Washington said the recent NATO cross-border helicopter strikes were not a strong-arm tactic aimed at pressuring Pakistan. The officials said the U.S. did not oppose the temporary closure at Torkham because it lets Pakistan rebuke Washington in a way that plays well to the domestic Pakistani audience without seriously hampering U.S. military operations. The officials spoke on condition of anonymity because they were not authorized to talk to the media. Since Pakistan closed Torkham, traffic has backed up at various points along the route from the southern port city of Karachi. But coalition officials say the closing has not resulted in shortages since hundreds of trucks still cross into landlocked Afghanistan each day through Pakistan and via Central Asian states. The convoys bring fuel, military vehicles, spare parts, clothing and other non-lethal supplies for foreign troops. ------ Associated Press Writer Riaz Khan in Peshawar and Anne Gearen in Washington, D.C. contributed to this report. 