A marine and two soldiers were killed in separate explosions, while an airman died in a vehicle accident near Camp Bastion, the main British military base.
In the first explosion, a member of the 40 Commando Royal Marines died while on foot patrol in the Sangin district of Helmand Province, southern Afghanistan, on Friday.
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The second blast killed a soldier from The Royal Dragoon Guards in the Nahr-e Saraj district of Helmand on Saturday. He was part of a patrol providing security to allow the construction of new roads and security bases, the MoD said.
Another soldier, from the Royal Logistic Corps, also died while helping clear a major route in southern Nahr-e Saraj on Saturday. He was working in a team dismantling roadside bombs when he was killed by an explosion.
Meanwhile, an airman from The Royal Air Force Regiment who was serving as part of the Camp Bastion Force Protection Wing in Helmand died on Friday in a traffic accident, military spokesman Lieutenant Colonel James Carr-Smith said.
The families of the dead have been informed.
Earlier this week, a renegade Afghan soldier killed three British troops on an army base in Helmand.
British Prime Minister David Cameron said last month he wants the country's combat troops to withdraw from Afghanistan within five years, without fixing a precise timetable.
A total of 322 British forces personnel or civilians working for the MoD have now died in Afghanistan since 2001. Britain has around 10,000 troops there as part of an international force fighting the Taliban.
