PESHAWAR — Pakistani security forces killed 18 Taliban militants Thursday in Bajaur region, a military official said, in the fourth straight day of fighting which has cast doubt on the effectiveness of crackdowns on militant groups. Pakistan’s military, one of the largest in the world, has launched a series of offensives against the Taliban over the past few years in Bajaur and other parts of the ethnic Pashtun tribal belt in the northwest near the Afghan border. On Wednesday, Taliban militants attacked an army post and killed eight soldiers in the South Waziristan tribal region. Military sources said four soldiers have been killed in the Bajaur fighting and several went missing. — Reuters