A man in an Afghan police uniform has shot and killed three British soldiers in southern Afghanistan, according to the UK defence ministry.

The three soldiers came under fire on Sunday at a checkpoint in Nahr-e-Saraj in Helmand province, where they were meeting local elders, the ministry said.

The American-led NATO coalition said a man in an Afghan National Civil Order Police uniform was responsible.

An ISAF spokesman said the gunman was wounded and detained after the attack, which happened around 5:00 pm (1230 GMT), and is now under investigation. The incident is not thought to have happened on an ISAF base, the spokesman said.

The spokesman added that ISAF was still investigating whether the attacker was a police officer or not.

Their deaths bring to 39 the number of foreign troops killed this month, and 215 so far this year.

Earlier, Afghan police said a roadside bomb killed five Afghan civilians in the eastern province of Ghazni.

Mohammad Hussain, the deputy provincial police chief major, said a bus full of people struck the explosives on Sunday morning while driving near Ghazni city, capital of the province of the same name.

He said another 11 people were wounded, and the dead included women and children. The bus was travelling from Kabul to the southern city of Kandahar.

NATO has around 130,000 soldiers fighting alongside some 350,000 Afghan security personnel, but they are due to pull
out of the country in 2014.

The Western forces is to hand over security to local forces by mid-2013 and will play a support role up to the final withdrawal by the end of the following year.