U.S. and Iraqi soldiers discovered a series of large underground bunkers used by insurgents to store weapons close to the restive western city of Fallujah, the U.S. military said Sunday. The underground facility, which was said to be the size of six football fields, was found to contain large quantities of arms and ammunition and is the biggest weapons seizure so far this year. Living quarters were also found underground, dpa reported. No insurgents were found when the system of bunkers was searched but the facility was used recently, a U.S. military spokesperson said. The entrance to the bunkers was found Thursday in a quarry at Karmah, close to Fallujah which has seen much fighting between U.S. forces and insurgents. It remained unclear whether the bunker was built by the former regime of Saddam Hussein or more recently, dpa reported. Meanwhile Iraqi authorities said they arrested a key deputy of top terrorist Abu Musab al-Zarqawi along with five other suspected insurgents in the northern city of Mosul on Friday.