KABUL: A teenage suicide bomber struck outside Nato headquarters in Kabul on Saturday, killing six people, including child hawkers, as Afghanistan marked a public holiday, officials said.

The Taliban, leading a decade-long insurgency against Nato troops and the Afghan government, swiftly claimed responsibility for the attack, saying the CIA had been the target.

The assault defied stepped-up Afghan security measures put in place across Kabul as government dignitaries commemorated 11 years since the death of Ahmad Shah Massoud, an iconic anti-Taliban commander two days before 9/11.

It was the deadliest attack in the fortified capital since Taliban fighters raided a nearby lakeside hotel on June 22, killing at least 18 people.

It is likely to renew questions about stability in Afghanistan as Nato combat troops withdraw from the country before an end-2014 deadline when they are due to transfer responsibility to their Afghan counterparts.

The blast reverberated through Kabul's diplomatic quarter, which is home to many Western embassies, shortly after First Vice President Mohammad Qasim Fahim finished an address to scores of dignitaries at an event mourning Massoud.

Afghan security forces sealed off the bomb site in front of Nato headquarters and close to the Italian embassy, an AFP reporter said.

“It was a suicide attack that killed six people and wounded five others,” interior ministry spokesman Sediq Sediqqi told AFP.

A senior police official speaking off the record gave the same death toll.

“It was a suicide bombing carried out by a young boy. So far there are six dead and five wounded. Most of the victims are young children who gather around ISAF to sell small items to soldiers leaving or getting into the base,” he said.

General Ayub Salangi, the Kabul police chief, confirmed four deaths.

“A 16-year-old boy on foot, blew himself up killing four and wounding two, all civilians. There are some children among the dead and wounded,” he said.

Taliban spokesman Zabiullah Mujahid claimed responsibility.

“It was one of our mujahedeen targeting CIA officials in Kabul. Many foreigners have been killed. I don't know the number yet,” he said.

The Taliban frequently exaggerate their claims.

A spokesman for Nato's US-led International Security Assistance Force confirmed only a blast and said that there had been no damage to Isaf headquarters or military casualties.

“We're aware of a blast that occurred just outside Isaf headquarters in Kabul this morning,” US Army Major Adam Wojack told AFP.

“There are no ISAF casualties. The ISAF compound is secure.” The Kabul attack came after separate bombings in the south killed two tribal elders and two women on Saturday.

US officials confirmed overnight that Nato withdrawals are on track with 117,000 foreign troops left in Afghanistan.

The United Nations says 1,145 civilians were killed in the war in the first six months of this year, blaming 80 per cent of the deaths on insurgents.