At least 45 terrorists were killed in Pakistan's restive northwest in one of the deadliest strikes by US drones, signalling Washington's resolve to step up assault on terror groups in this country despite growing strains in ties with its key ally. The unusually heavy barrage of three missile strikes in a span of 12 hours, targeting militant hideouts in north and south Waziristan took one of the largest death toll in the controversial unacknowledged air campaign. The drone attacks commenced on Monday night when unmanned aircraft unleashed nine missiles into a suspected militant compound and a vehicle in north Waziristan, killing 25 terrorists, local officials were quoted by TV channels as saying. Few hours later, the drone struck again in nearby South Waziristan firing missiles and killing five terrorists. The drones reappeared early this morning over the area firing two missiles at another compound in North Waziristan killing 15 terrorists. It was the second largest death toll in drone campaign.