Reports from Afghanistan say a large explosion has rocked the capital, Kabul, near government buildings including the headquarters of the national intelligence service.

Witnesses said Wednesday's blast was followed by the sound of gunshots, and a plume of smoke was reported rising into the sky. It was not immediately clear whether there were any casualties.

The blast comes just days after Afghan President Hamid Karzai returned from a trip to Washington, where he held talks on Afghan security with U.S. President Barack Obama.