ADEN - Yemeni troops backed by tanks and helicopters assaulted an eastern city on Wednesday to drive out al-Qaida-linked militants who had planned to set up an Islamist emirate there, a local official said.Three soldiers and several militants were killed in the fighting at Ghail Bawazeer, north of the Hadramout provincial capital of al-Mukalla. Clashes began early in the morning involving dozens of soldiers, the official said.Ambulances transported casualties to hospitals as residents stayed home to avoid being caught in the battle.