Pakistani troops launched an offensive in the Kurram tribal district near the Afghan border, forcing thousands of families to flee, security officials and relief workers said Monday. The operation was aimed at Tehrik-e-Taliban Pakistan, an umbrella organization of more than a dozen militant outfits believed to be behind the killings of thousands of civilians and security personnel since 2007, reported DPA. A senior officer at the paramilitary Frontier Corps Force said troops backed by tanks, artillery and gunship helicopters moved into the district. Fighting is going on since yesterday but we don't know the casualties so far,' said the official who spoke on condition of anonymity. The offensive forced around 4,000 families to flee the region. Mujahid Turi, a coordinator of the government relief organization Fata Disaster Management Authority, said 500 families had enrolled. 'The rest are believed to have moved with the relatives and friends at safer places.' Hundreds of militants moved into Kurram following military operations in neighboring districts of Orakzai, Khyber and South Waziristan. They have intensified the ongoing conflict between Shia and Sunni tribesmen in the region, leaving hundreds of dead.