Afghan police say a car bomb has exploded in the capital, Kabul, just hours after U.S. President Barack Obama left the city following an unannounced visit.

Kabul's police chief said Wednesday's car bombing hit Jalalabad road, the main road to the east of the capital. The area hosts several U.S. military bases and housing compounds.

It is unclear if the bombing caused any casualties. The U.S. embassy warned staff to take cover.

Witnesses heard at least one other explosion in the eastern part of the capital. Gunfire followed the blasts.

During Mr. Obama's quick visit, he signed the Strategic Partnership Agreement with his Afghan counterpart, Hamid Karzai.