A suicide bomber has killed at least 12 people and injured a number of others outside an army base in Kabul, Afghan security officials say.
Security forces quickly sealed off the blast area
The suspected bomber was among those killed in the powerful rush-hour blast, near the army training centre.
A security official said the bomber drove his motorbike to a car park where Afghan soldiers were waiting for buses.
There have been several suicide bombings in Afghanistan this year, but they are relatively rare in Kabul.
The last one in the capital in May killed three people.
Wednesday's was the first such incident in the country since parliamentary elections on 18 September.
Afghan President Hamid Karzai was swift to extend his sympathies to the victims.
"I am saddened that the lives of many Afghan people, mainly soldiers serving the Afghan nation were lost. I condemn it in the strongest terms."
Defence Ministry spokesman Mohammed Zahir Azimi had earlier said: "Today just after 1630 (1200 GMT) a man riding on a motorbike carried out a suicide attack in front of the Kabul military training centre."
He said initial reports suggested a number of those killed were Afghan National Army soldiers.
Nato-led peacekeepers, who have a base 500 metres away, and Afghan police sealed off the area, causing huge tailbacks of traffic.
The BBC's Bilal Sarwary at the scene of the attack on the Kabul-Jalalabad road said there was chaos after the blast.
At least three army buses were seriously damaged, he said.
Witnesses spoke of scenes of horror.
"I saw a man on a motorbike driving towards the parking area where there were a lot of soldiers trying to get into a bus. I heard a big bang and every one started running. Then I saw people lying on the road," Mohammad Haider, a 31-year-old taxi driver, told the BBC.
The bomber struck at one of the busiest hours in the day, with hundreds of people outside the centre after work.
"It was rush hour and I was waiting with everyone for their buses to go home, when I saw a motorcycle rushing towards lots of buses and people in the parking area," an Afghan army officer told the AFP news agency.
"Suddenly I heard a huge boom. I fell to the ground and when I stood up I saw several bodies scattered around.
"Two buses were on fire and there was human flesh around me."
It is not yet clear who was behind the attack but Abdul Latif Hakimi, who claims to speak for the Taleban, said they carried it out. He named the bomber as Sardar Mohammad and threatened more attacks.
Earlier in the day, Afghan intelligence officials told the BBC they had information that an al-Qaeda suicide squad - Fedayini Islam - was in Afghanistan.
Officials said they suspected the bomber might have been Arab.
There have been other suicide bomb attacks this year in Afghanistan. In May a UN worker and two others died in an attack on a Kabul internet cafe.
A suicide bombing in Kandahar left more than 20 people dead in June.
The last major explosion in Kabul was in August 2004, when a car bomb ripped through the office of a US contractor providing security for President Hamid Karzai, killing about 10 people. The Taleban said they carried out the attack.
Last October three people died in the capital when a suicide bomber detonated hand grenades as he approached soldiers in a busy shopping street.
More than 1,000 people have been killed in violence linked to militancy in Afghanistan this year.