The explosion took place soon after new US Defense Secretary Chuck Hagel arrived in the country.
CNN writes that the explosion took place as Hagel was giving a press conference, forcing the event to move to a safer location.
According to the BBC, the explosion was followed by "the sound of heavy gunfire," while Kabul police chief Mohammad Zahir said that the situation was under control, and victims had been transported to area hospitals.
The attack took place around 9:00 AM, carried out by a suicide bomber riding a bicycle, writes CBS, and authorities are stll trying to ascertain the number of casualties, which CBS lists as seven killed and six wounded.
"We are still at war," said Hagel at the March 9 press conference.
"That transition has to be done right, it has to be done in partnership with the Afghans, with our allies," he added. "Our country as well as Afghanistan, the region, and the allies have a lot at stake here. And our continued focus and energy and attention on Afghanistan is going to be very important."