A suicide bomber has killed at least six people near the headquarters of the Nato-led international coalition (Isaf) in Kabul. A number of children are among the dead. There were no reports of casualties among Isaf troops. An attacker on a motorbike blew himself up near the entrance, an Isaf spokeswoman told Reuters news agency. Kabul security has been tightened as supporters of an anti-Taliban warlord mark 11 years since his assassination. Ahmad Shah Massoud - a hero of the 1980s war against Soviet occupiers, and later of opposition to the Taliban - was killed by al-Qaeda suicide bombers on 9 September 2001. Following Saturday's explosion, the Isaf HQ at Camp Eggers, which is home to some 2,500 personnel, was placed "on lockdown", the Isaf spokeswoman said. 'Child hawkers' Afghan police confirmed a suicide bomber had struck. Child street hawkers are believed to have been caught in the blast and witnesses quoted by Reuters said small bodies could be seen being carried to ambulances. A police official speaking on condition of anonymity told AFP news agency: "Most of the victims are young children who gather around Isaf to sell small items to soldiers leaving or getting into the base." The US embassy, the Italian embassy and the presidential palace are also located near the site of the attack. A Taliban spokesman named Zabihullah Mujahid said the militant group had carried out the attack, targeting US intelligence. Scores of dignitaries are due to attend commemorations of Massoud's death in Kabul on Saturday, which is a national public holiday in his honour.