At least two U.S. soldiers and two unidentified attackers were killed and nine other American troops were injured in a firefight early Tuesday in Fallujah, the U.S. military said. Maj. Randy Martin, a spokesman for the U.S. Army's V Corps said that six Iraqis were captured and were being interrogated. The attackers used rocket-propelled grenades and small arms in the attack, a statement from U.S. Central Command said, but Martin said the grenade was thrown by hand. "Who knows what they were thinking when they engaged U.S. soldiers?" Martin said. "I know we suffered casualties, and the enemy paid a price for those casualties." Martin said the Americans hit were at a traffic-control point just after midnight with gunfire from occupants of one of two vehicles that had pulled into the checkpoint together. U.S. soldiers were searching the first vehicle and had just found weapons inside when the occupants of the accompanying vehicle opened fire and threw a grenade. "Fire opened up from all directions," Martin said. U.S. troops responded with fire from Bradley Fighting Vehicles, machine guns and small arms. They killed two of the attackers and captured six others, the statement said. An Army helicopter landed during the firefight to evacuate the wounded and was damaged when a Bradley struck it while maneuvering into a firing position. The wounded soldiers were evacuated to a military aid station in the area. The names of the two dead soldiers were not immediately released. "Fallujah has been an area of concern for us," Martin said. But he said conditions had been improving before Tuesday. Protests against the Army's presence in Fallujah turned violent when U.S. soldiers fired on crowds on April 28 and April 30, killing 18 Iraqis and wounding at least 78. The soldiers said then that they were defending themselves and the crowd fired first, but Iraqis said no shots were fired at the Americans. No Americans were wounded by gunfire. Meanwhile, a U.S. soldier died Tuesday and two others were injured in a road accident near the town of Talil, when their tractor-trailer collided with another vehicle. Another man drowned after diving into an aqueduct in northern Iraq, the Central Command said. The deaths came after one of the most violent days for U.S. troops in recent weeks. A soldier was killed Monday and another wounded when their convoy was ambushed in northern Iraq, and four soldiers were hurt in what appeared to be a land-mine attack in a Baghdad neighborhood. On Sunday, a U.S. soldier was killed and another injured in southern Iraq when a munitions dump they were guarding exploded. The blast was not thought to be a result of hostile action, Central Command said. **PHOTO CAPTION*** An Iraqi man walks by the wreckage of a US Army Humvee left in a street in Baghdad at the site where a US soldier was killed and four others wounded.(AFP/Patrick Baz)