KABUL: An Afghan official says a group of suicide bombers have attacked U.S. base near the border with Pakistan, sparking an ongoing gunbattle. There was no immediate information on casualties. Ahmad Zia Abdulzai, spokesman for the governor of Nangarhar province, says the heavily armed militants attacked the site in the Torkham area Monday morning. An explosion heard toward the beginning was likely one of the suicide bombers detonating his explosives. Taliban spokesman Zabiullah Mujahid says the insurgent group was behind the attack. NATO says it has no immediate information on the matter. Abdulzai says Afghan and U.S. forces are engaged in gunfire against the militants, and that NATO helicopters are flying over the base. The highway between Jalalabad city and Torkham, an important route for NATO supply trucks, has been closed.