Four US soldiers were killed and three wounded in a bomb explosion in Southern Afghanistan on Sunday, said media reports. Reports citing a US military statement, issued in capital city of Kabul, said that a roadside bomb exploded in Daychupan district of Zabul province when the Afghan and the US troops were conducting an operation against Taliban rebels. Maj. Gen. Jason Kamiya, the U.S.-led coalition's operational commander, in the statement said that the three wounded soldiers were hit by shrapnel and were in stable condition."The unit was conducting offensive operations in support of an ongoing mission to find and defeat enemy forces in the area when the attack occurred," the statement said. "The unit's mission is part of a much larger operation to disrupt enemy forces and to thereby provide a safe environment for upcoming September elections", the statement said, adding, the attack would strengthen, not weaken, the resolve of the troops.