A suicide bomber has attacked a bus carrying Afghan soldiers to work in the capital, Kabul, wounding at least nine people, officials have said.

The Kabul police chief's office said in a statement that the early Wednesday morning blast in western Kabul came from a man on foot wearing a suicide vest who detonated his explosives as he approached the bus.

Most of the wounded are believed to be army personnel.

"At around 7:10am local time [02:40 GMT], a suicide attacker on foot detonated himself next to a military bus in third district of Kabul city," Hashmatullah Stanikzai, police spokesman, said.

Dawlat Waziri, deputy spokesman at the defence ministry, said the bomber was on foot and tried to board the vehicle.

"But when he was prevented, he detonated himself outside the bus, injuring five officers and one civilian," he told AFP news agency.

A spokesman for the Taliban, which is leading an 11-year fight against the Western-backed government, claimed responsibility for the attack.

The attack comes three days after a would-be car bomber was shot dead by police in downtown Kabul. That assailant was driving a vehicle packed with explosives and officials said he appeared to be targeting an intelligence agency office nearby.

Meanwhile, the Pentagon admitted on Tuesday that NATO's International Security Assistance Force had wrongly reported a seven percent decline in Taliban attacks last year, saying that the number was roughly the same as in 2011.

"This is a regrettable error in our database systems that was discovered during a routine quality check. We are making the appropriate adjustments," Pentagon spokesman George Little said.

The accurate number for attacks in 2012 showed the assaults had remained at the same level as in 2011, at more than 3,000, a US defence official said.

The United States and NATO have about 100,000 troops in Afghanistan, but the vast majority will leave next year, with an estimated 352,000 NATO-trained Afghan police and soldiers taking over.

Source: Agencies