Juba - An American man has been killed in civil war-torn South Sudan, the US Embassy said on Saturday, while South Sudan's army said he was caught up in fighting between rebels and government forces.Embassy official Jeremiah Knight confirmed the man's death to The Associated Press, with no further details. The body was at the military hospital in South Sudan's capital, Juba, until next of kin were notified.South Sudan army spokesperson Colonel Domic Chol Santo told the AP that the man was killed on Saturday morning when opposition rebels attacked the town of Kaya on the Ugandan border.The man was "caught in the fighting" that also left 15 rebels dead, the army spokesperson said.The opposition said it was looking into the reports. It was not immediately clear why the American was there.South Sudan's civil war is well into its fourth year, with tens of thousands of people killed. The fighting, often along ethnic lines, defies peace deals and unilateral cease-fires.Millions of people have fled the oil-rich but impoverished East African nation, creating what has been called the world's fastest-growing refugee crisis. More than a million have fled across the border into Uganda, while fighting has flared in the border area.The international community has struggled to find ways to end the conflict. Late last year, a US-led attempt to have the UN Security Council impose an arms embargo on South Sudan failed with insufficient support. Both sides in the civil war have been accused of abuses.