Hagel was in official meetings at a coalition military headquarters not far from the ministry when the explosion occurred. This is Hagel's fifth trip to Afghanistan, but his first as Secretary of Defense. Here Hagel presents a purple heart to a soldier in Jalalabad, Afghanistan. Photo Credit, Chuck Hagel's Flickr.

Afghan Defense Ministry spokesman, General Zahir Azimi, said a suicide bomber riding a bicycle detonated an explosives-filled vest he was wearing. The blast "unfortunately caused a number of civilian casualties," but "no military personnel were killed."

A spokesman for the international forces in Afghanistan, Charlie Stadtlander, said U.S. Defense Secretary Chuck Hagel was not near the explosion when it happened. 

The Taliban said it carried out the blast as a "message" for Hagel, who arrived Friday on his first visit to Afghanistan--saying it was an attempt to prevent Hagel from “spreading lies” about the insurgency’s weaknesses.

Hagel referred to the blast in comments to reporters and expressed condolences to the victims, reports CNN.

"I wasn't sure what it was," he said. "I was in a briefing... but we're in a war zone. I've been in war. So, shouldn't be surprised if a bomb goes off or an explosion."

READ MORE: Chuck Hagel Confirmed As Pentagon Head After Senate Vote

Half an hour after the Kabul explosion, another suicide bomber struck at a checkpoint in Khost province, killing eight children and a policeman, according to Afghan military and hospital officials.

There was no immediate claim of responsibility for that blast.

Read more on the recent suicide attacks in Afghanistan and U.S. Defense Secretary Chuck Hagel's trip here.

Follow Executive Producer Chima Simone on Twitter.