The militants said the attack was carried out to punish Afghan judges for sentencing to death Taliban prisoners held by the Afghan government.
"Today's attack was a warning should they (judges) continue to give tyrannical verdicts and intimidate (our) countrymen," said a copy of their statement sent to AFP.
A suicide car bomber rammed a bus packed with staff of Afghanistan's top court, killing 14 and wounding 38 in the second attack in two days in the heavily fortified capital, police said.
General Mohammad Zahir, head of Kabul criminal investigations, said the bomber rammed a bus carrying Supreme Court staff. Officials said it happened at around 4 pm (1130 GMT), which is the end of the working day in Afghanistan.
"A suicide bomb hit at the back of a Coaster causing lots of civilian casualties, dead and wounded. I'm at the scene and can't talk more," Zahir told AFP.
"We have 14 dead and 38 wounded. It was a car bombing that directly hit the Supreme Court bus."
An AFP photographer saw the wreckage of a car, mangled buses and shattered, burnt bodies of the victims on the main road leading to the airport.
Yesterday seven Taliban insurgents were killed after launching a gun and grenade attack on military buildings near the airport's perimeter fence.
The response from Afghan security forces to that assault was widely praised as a sign of their growing professionalism, as they take over responsibility from 100,000 US-led foreign combat troops who will pull out by the end of next year.
