NATO officials say Afghan militants fired rockets on a U.S. airbase in Afghanistan early Tuesday, damaging a plane used by America's top military officer.

U.S. Joint Chiefs of Staff chairman Gen. Martin Dempsey was not on board at the time. He later left the base using another plane. The attack slightly wounded two ground staff.

Sporadic shelling is not uncommon at Bagram Airbase. But Taliban insurgents rarely inflict serious damage or casualties at the facility, north of Kabul.

NATO spokesmen said the attack posed no threat to the safety of Dempsey or his staff, who they said were “nowhere near” the aircraft when two rockets landed near where it was parked.

Dempsey had arrived in the country Monday for talks with NATO and Afghan commanders that focused on a series of recent killings of international troops by Afghan security forces.

In Washington Monday, U.S. President Barack Obama said he is concerned about the so-called “green on blue” attacks.

Afghan security forces have killed 10 international troops, mostly Americans, in the past two weeks. In the latest incident Sunday, a person wearing an Afghan police uniform shot and killed a coalition service member. At least 39 international coalition members have been killed in such attacks this year.