An explosion has sent smoke rising over the heart of Afghanistan's capital. The strong blast was felt several kilometers (miles) away.

An Associated Press cameraman who witnessed Friday's blast said it was near a hospital for the National Security Directorate, the state intelligence service. He said the blast collapsed a building wall, but was not clear if there were any casualties. Police quickly cordoned off the area, which also houses buildings used by international aid agencies.

Police officer Latif Khan, director of the city's district 4, said he was on the way to the scene but had no other information.

It is the second explosion to hit Kabul in just over a week.