Three Georgian soldiers have been killed in southern Afghanistan after fighters detonated a vehicle laden with explosives, according to a senior Western military official and NATO.

The death toll of the number of Georgian troops in Afghanistan increased to 22 after Monday's attack, which targeted their base in Helmand province.

"Two Georgians died on the spot, a third died of wounds," the senior Western military official in Kabul, speaking on condition of anonymity, said.

Georgian media quoted Irakly Alasania, the country's defence minister, as saying that a suicide bomber drove a lorry full of explosives into their base.

In another separate incident on Monday, 10 civilians, mostly women and children, were killed when a roadside bomb hit the bus they were travelling in in Maroof district, roughly 60km northeast of Kandahar city.

Georgia, which has more than 1,500 soldiers serving in Helmand, has the largest non-NATO combat troop commitment in Afghanistan.

May has proved particularly bloody for members of the NATO-led International Security Assistance Force (ISAF), which is preparing to withdraw all combat troops by the end of next year.

The blast also wounded 12 people.