A U.S. soldier was killed and two others were slightly wounded when their convoy was attacked in southern Afghanistan, the U.S. military said Sunday.

Afghan authorities said they had arrested two Taliban suspects in the attack, which occurred Saturday in Helmand province. They also reported that U.S. forces defused a bomb Saturday at a bridge in the same province.

In neighboring Kandahar province, Afghan police seized 80 assault rifles being smuggled in an oil truck, and hundreds of Afghan forces were deployed to tighten security.

The two U.S. soldiers injured in the attack on the patrol near Girishk in Helmand returned to duty after medical treatment, said Lt. Col. Michele DeWerth, a U.S. military spokeswoman in the Afghan capital, Kabul. She did not identify any of the soldiers.

DeWerth said one "anti-coalition" fighter was detained. However, Dad Mohammed Khan, the intelligence chief for Helmand, said that Afghan officers had arrested two suspected Taliban fighters in the attack, which he said happened about 20 miles northeast of Girishk.

The last reported U.S. fatality in Afghanistan was on May 7, when a Marine was killed in a nighttime attack on a patrol in southern Uruzgan province.

On Saturday evening, U.S. forces defused a bomb over a river in Girishk, said district police chief Bier Jan. "Terrorists wanted to blow up this bridge," he said. "We got information, we found this bomb and told U.S. forces, who came and defused it."

He said that six suspects, whom he did not identify, had been arrested and that an investigation was underway.

On Sunday, Afghan police arrested six suspected Taliban fighters for smuggling weapons in Kandahar.