A Taliban bomb attack Wednesday destroyed 22 fuel tankers carrying supplies for NATO forces in Afghanistan, local officials said. A pre-dawn explosion triggered a fire which engulfed the trucks, parked in the northern province of Samangan overnight on their way from Uzbekistan towards NATO forces in the south, Samangan deputy governor Ghulam Sakhi Baghlani said. "The first explosion resulted in a fire which quickly engulfed as many 22 trucks," he said, adding that three drivers were also injured in the blaze. NATO was forced to make greater use of more expensive northern supply routes after Pakistan banned NATO traffic following a botched US air strike which killed 24 Pakistani soldiers last November. Taliban insurgents fighting to overthrow the Western-backed government of President Hamid Karzai claimed responsibility for the attack, saying several private guards were killed. A spokesman for NATO's International Security Assistance Force (ISAF) said initial reports showed 24 tankers were destroyed after an improvised bomb attack. But he said he could not immediately confirm that the civilian tankers were carrying fuel for ISAF, which relies on contractors to move many of its supplies. Pakistan lifted its blockade on NATO supplies earlier this month, but only a few trucks have actually crossed the border. Owners say they are waiting for compensation and security guarantees in the face of Taliban threats before resuming journeys from the Arabian Sea port of Karachi to the Afghan border. ISAF spokesman Brigadier General Gunter Katz said this week that there had been an increase in insurgent attacks in Afghanistan recently. "Generally, in the past 12 weeks, we have a slight increase, 10 percent, of insurgent attacks on Afghan security forces and international troops," he told a news conference. Two NATO soldiers were killed in an improvised bomb attack in eastern Afghanistan Wednesday, ISAF said in a statement, taking the total number of deaths this year to at least 242, according to a tally by the icasualties.org website. Two others were injured in a helicopter crash in western Afghanistan. The cause of the incident was under investigation, the coalition said. NATO has about 130,000 troops helping the government of President Hamid Karzai fight a Taliban insurgency, but they are due to withdraw by the end of 2014.