Militants ambushed an Afghan police vehicle, killing two on Saturday and a coalition helicopter crashed in eastern Afghanistan with no fatalities, NATO and Afghan officials said. The Afghan Ministry of Interior said insurgents attacked the policemen in Dara Nur district in the northern tip of Nangarhar province. Two others were wounded in the attack, the ministry said. Fighting has escalated in eastern Afghanistan as Afghan and coalition forces step up their attacks on insurgents along the Pakistan border and militants retaliate with attacks on pro-government forces and Afghan officials. A suicide attacker on foot detonated his vest packed with explosives Friday afternoon at the entrance to a building used by education officials in Jayi Maydan district of Khost province, said Abdul Hakim Ishaqzai, police chief in the eastern province. The bomber died in the attack and four people were wounded, including the district education director and a local principal, he said.