About a half hour later, another suicide bomber attacked a police checkpoint in Khost, the capital of Khost province in eastern Afghanistan. An Afghan policeman and eight civilians, who were mostly children, died in that blast, said provincial spokesman Baryalai Wakman.
"We are still at war," Hagel said shortly before he arrived on Friday, the same day that three men wearing Afghan army uniforms and driving an Afghan army vehicle forced their way onto a U.S. base in eastern Afghanistan and opened fire, killing one civilian contractor and wounding other U.S. troops.
On Saturday, a U.S. military official identified the dead contractor as an American citizen, and added that four U.S. soldiers were injured in the attack. The official said investigators were "95 percent certain it was an insider attack," because the three men came from the Afghan side of the joint U.S.-Afghan base, and rammed an Afghan army Humvee through a checkpoint dividing the base, before jumping out and opening fire on the Americans with automatic weapons. All three attackers were killed.
The official spoke on condition of anonymity because he was not authorized to speak publicly.
The Taliban said it was not behind the Tagab attack, but the group claimed responsibility for the morning attack at the ministry, saying it was meant to send a signal to the U.S. defense chief.
"This attack was a message to him," Taliban spokesman Zabiullah Mujahid said in an email to reporters.
Pentagon spokesman George Little said Hagel was in a briefing at a U.S.-led military coalition facility in another part of the city when the explosion occurred. He said the briefing continued without interruption.
Afghan Defense Ministry spokesman Gen. Mohammad Zahir Azimi said the bomber on a bicycle struck just before 9 a.m. local time about 30 yards from the main gate of the ministry.
A man at the scene, Abdul Ghafoor, said the blast rocked the entire area.
"I saw dead bodies and wounded victims lying everywhere," Ghafoor told AP Television News. "Then random shooting started and we escaped from the area."
The ministry said at least nine civilians were killed and others were wounded.
Reporters traveling with Hagel were in a briefing when they heard the explosion. They were moved to a lower floor of the same building as U.S. facilities in downtown Kabul were locked down as a security precaution.