Pakistan has lodged a formal complaint with the US over a deadly ground attack inside its borders. Pakistani officials say at least twenty civilians were killed after helicopters delivered a US-led unit into Pakistan. US forces are said to have fired inside three homes containing women and children. The attack marks the first time the US has used ground troops inside Pakistan. A Pakistani government statement condemned what it called a “gross violation of Pakistan’s territory” and “a grave provocation.” US officials have declined comment so far. The attack comes less than two weeks after a US air strike in Afghanistan killed as many as ninety civilians, including sixty children. The US has disputed the casualty toll.