PARACHINAR, Pakistan, Feb 18, (AP): Militants in Pakistan overnight ambushed security forces who were responding to an earlier attack on aid trucks in the country's troubled northwest, leading to a shootout in which four troops were killed, officials said Tuesday. The ambush happened hours after authorities dispatched reinforcements to respond to Monday's attack on a convoy of aid trucks in which a driver and security official were killed in Kurram, a district in the restive Khyber Pakhtunkhwa province.

Some security forces were also wounded in the overnight ambush in Kurram, where at least 130 people have died in recent months in clashes between rival Shiite and Sunni tribes, officials said. Several trucks that were heading to Parachinar, the main city in Kurram, were looted and burned, authorities said. Qaiser Abbas, a doctor at a hospital in Parachinar, said they received the bodies of four security forces Monday night from Kurram, where authorities noted a large-scale operation was being planned to try to apprehend the perpetrators of the attacks.

No group has claimed responsibility for the latest attacks but suspicion is likely to fall on Sunni militants. Shiite Muslims dominate parts of Kurram, although they are a minority in the rest of Pakistan, which is majority Sunni. The area has a history of sectarian conflict, with militant Sunni groups previously targeting minority Shiites.