HERAT, Afghanistan—A fuel tanker exploded Saturday at the Islam Qala crossing in Afghanistan’s western Herat province on the Iranian border, injuring at least seven people and causing a massive fire that consumed more than 500 trucks carrying natural gas and fuel, according to Afghan officials and Iranian state media. It wasn’t immediately clear what caused the blast. Wahid Qatali, Herat’s provincial governor, said Afghan first responders did not have the means to put out the huge fire and had requested support from Iran in the form of fire-fighting aircraft. “For the time being, we can’t even talk about the casualties,” Qatali told The Associated Press. The intensity of the flames meant ambulances were having trouble reaching the wounded or getting close to the site of the blast, said Mohammad Rafiq Shirzy, spokesman for the regional hospital in Herat’s provincial capital, also named Herat. Seven people injured by the fire have …