One US soldier was killed and three others were wounded in a bomb blast in southern Afghanistan Saturday, US military spokeswoman Lieutenant Cindy Moore told AFP. The casualties occurred during an armoured vehicle patrol in Shinkay district in the restive southern province of Zabul when an improvised explosive device detonated, Moore said. Two of the soldiers were evacuated by helicopter to Kandahar for treatment, the US military said in a statement. "One died of his wounds at Kandahar. The other is in critical but stable condition and was in surgery at 6:30 pm (1400 GMT)," it added.