A suicide bomber blew himself up outside the gates of a US base in eastern Afghanistan on Monday, killing nine Afghan civilians and wounding thirteen, officials said. The blast came as the top US official in eastern Afghanistan, Maj. Gen. Jeffrey J. Schloesser, warned that militants would attack military, civilian and government targets during Afghanistan's Independence Day celebrations. The bomber in Khost province rammed his explosives-laden vehicle at the gates of the American military base in Khost city, said Arsallah Jamal, the province's governor. US military said the attack did not penetrate the base's perimeter. All victims were civilian, Jamal said. A second bomber tried to ram the police who were investigating the first blast, but was shot dead by officers, he added. US troops provided medical care to the wounded, the US-led coalition said in a statement. Militants regularly use suicide attacks against Afghan and international forces, but the majority of victims in such attacks are civilians. In other violence, a bomb blast in the eastern province of Nangarhar killed two police on a patrol late Sunday, said Ghafor Khan, spokesman for the provincial police chief. Several militants were killed in two separate clashes with US-led coalition troops in the eastern provinces of Kapisa and Paktika on Sunday, the coalition said. It did not provide an exact number of the militants killed. More than 3,300 people - mostly militants - have been killed in insurgency-related violence this year, according to figures from Western and Afghan officials.