June has become the deadliest month for foreign forces in Afghanistan since the start of the war in 2001.

So far 79 Coalition troops have lost their lives in Afghanistan this month, including five Australians.

In the latest incident, four British soldiers were killed in a vehicle accident in the southern province of Helmand.

Coalition casualties are escalating amid the arrival of thousands of extra United States and Coalition troops as part of US president Barack Obama's surge strategy.

Coalition commanders are warning of more casualties when the number of foreign troops is expected to peak in August.