Assailants threw a bomb at a police checkpoint in eastern Pakistan before dawn Saturday, killing seven officers, police said. District Police Chief Malik Tassadaq Hayyat said the attack came near the town of Mianwali in eastern Punjab province. He said residents also heard gunfire before the explosion that knocked down the roadside checkpoint. Hayyat would not say who could be behind the attack but said it was "an act of terrorism" and officers were still investigating. Mianwali lies at the edge of Pakistan's troubled North West Frontier Province, where police and troops have been fighting pro-Taliban militants since soon after the Sept. 11, 2001 attacks in the United States.