Blast heard in Afghan capital after Obama leaves

An explosion was heard in the Afghan capital, Kabul, on Wednesday, hours after US President Barack Obama left Kabul following an unannounced visit during which he signed a strategic partnership agreement.
Reuters journalists heard an explosion and police said they were investigating a blast in eastern Kabul. Obama left earlier after making a televised address to Americans from Bagram Air Base north of the capital.
A US embassy warning system urged staff to stay away from windows and take cover. The embassy is in the main diplomatic area in the center of the city.