A Taliban suicide bomber in Kabul has killed eight military officers in an attack on an air force bus, Afghan officials said.

It is the latest strike against the national security forces as US troops withdraw.

The Afghan capital has been relatively peaceful since the presidential election on 14 June, though there have been street demonstrations as politicians are locked in a dispute over vote fraud.

A defence ministry spokesman confirmed the death toll and said the attack struck at 7am (3.30am Irish time) as military staff were being taken to work.

The Taliban used a recognised Twitter account to claim responsibility for the blast, adding that the suicide attacker approached the vehicle on foot before detonating his explosive-packed vest.

A Taliban spokesman said that at least 25 people had been killed on the bus, though the insurgents regularly exaggerate death tolls after attacks.

Election day saw a sharp rise in nationwide violence, but there has not been a major attack in Kabul since 7 June, when 12 people were killed in a suicide strike against presidential candidate Abdullah Abdullah, who escaped unharmed.

Mr Abdullah has said he will reject the result of the on-going election vote count, alleging massive fraud against him in the race against his rival Ashraf Ghani.

NATO's 50,000-strong combat force will leave Afghanistan by December, though about 10,000 US troops will stay into next year if the new president signs a security deal with Washington.