A guard inspects the site of the suicide bombing in the heavily fortified international zone in the capital. The Taliban asserted responsibility for dispatching the bomber, whom officials described as 14 years old. He detonated his explosives about 150 feet from theheadquarters of the NATO-backed International Security Assistance Force. The blast killed six civilians, including several children, according to officials and eyewitnesses. (Richard Leiby/The Washington Post)

A suicide bomber killed at least six people, most of them children, in one of the Afghan capital’s highest-security zones when he detonated his explosives Saturday not far from the walled headquarters of NATO-backed military forces, witnesses and officials said.

No foreign troops were among the dead, the military coalition said. Reports conflicted over how the bomber entered the area, but it is readily accessible via a street closed to most vehicles but frequented by pedestrians and cyclists.

The Taliban asserted responsibility for the attack, saying it was carried out in response to the U.S. announcement Friday that it would designate the Taliban-allied Haqqani network as a foreign terrorist organization, freezing the group’s assets in the United States, among other sanctions.

The bomber, described by Kabul police as 14, detonated his explosives about 150 feet from the headquarters of the International Security Assistance Force, the coalition made up mostly of U.S. troops.

Several sensitive facilities — including a CIA station, the Italian and Spanish embassies and an installation of the Afghan spy service — abut the street. Their entrances are heavily guarded, but no security barriers to the street itself were in place even a few hours after the noonday blast, when a reporter visited the scene.

Nazar Mohammad, a 48-year-old watchman, said he narrowly escaped a suicide bombing that killed six people and destroyed a real estate and travel office. Mohammad said he usually sits on the steps of the office every day but was just down the street at the time. “It was God’s decision that I should live,” Mohammad said. (Richard Leiby/The Washington Post)

Afghan children are common in the international zone, where they hawk scarves, trinkets, cellphone cards and gum to foreigners. The explosion killed at least four children, people at the scene said, along with two shopkeepers. Small sandals, glass and wreckage on the sidewalk were mingled with rain puddles tinted by blood.

“I heard a big explosion and saw black smoke in the sky, and then when I came over I saw the bodies of the children,” said Nazar Mohammad, a 48-year-old watchman who has lodgings behind a real estate and travel office that was destroyed in the blast.

He said he counted six small bodies and two adult dead. The Interior Ministry said five people were wounded.

Normally, Mohammad passes a lot of time sitting on the sky-blue steps of the office. But he was down the street when the blast happened. “It was God’s decision that I should live,” he said.

The Haqqanis, based in Pakistan, have been linked to several deadly attacks in Kabul, dispatching suicide bombers and gunmen to assault Afghan government and international facilities, among them the U.S. Embassy. The attacks underscore the insurgents’ ability to inflict terror in the heart of the capital even after 11 years of a U.S.-led war to defeat them.

The bombing came as Afghans celebrated a national holiday marking the Sept. 9, 2001, assassination of anti-Taliban commander Ahmed Shah Massoud, whom al-Qaeda specifically targeted just before its terrorist attacks on the United States, which spurred the U.S. invasion of Afghanistan.

Officials said security forces were on high alert in anticipation of the commemoration.

The Taliban said the bomber arrived on foot, and it denied that he was a minor. The “martyrdom-seeking hero” was 28 and specifically targeted the offices of the CIA, Taliban spokesman Zabiullah Mujahid said on Twitter.

In a phone interview from an undisclosed location, Mujahid said the attack was a response to the U.S. action against the Haqqani network.

A spokesman for the international forces, Brig. Gen. Guenter Katz, condemned the attack, calling the insurgents’ tactics “despicable,” especially given reports that the bomber was a teenager.

“By taking advantage of an impressionable child to carry out this attack, the insurgents display cowardice,” Katz said in a statement. “Attacks like these exploit vulnerable individuals, coercing them into committing horrible acts.”

Javed Hamdard contributed to this report.