Four British troops were killed in two separate explosions in troubled southern Afghanistan, the Ministry of Defence said.
"Four Royal Marines were killed in two separate incidents in the Sangin area of Helmand province on Friday morning," the MoD said in a statement.
In the explosion which occurred south of the town of Sangin, three marines -- two from 45 Commando and one from Commando Logistics Regiment -- were killed yesterday.
"They were taking part in a routine operation against enemy forces in the area," the MoD said.
One marine died instantly, a second died of his wounds before he could be evacuated and the third died of his wounds in the hospital at Camp Bastion, Britain's main base in Afghanistan.
British newspapers said today that a 13-year-old boy was pushing a wheelbarrow in which a bomb was hidden. Reports said the teenager also died but it was unknown whether the bomb was detonated remotely.
The other explosion took place in the Sangin area. One soldier from 45 Commando, who was taking part in a routine patrol, was killed as a result. He died of his wounds while being taken to Camp Bastion.
The next of kin have been informed.
Prime Minister Gordon Brown paid tribute to the soldiers killed.
"Our thoughts are with the families and friends of these brave men who died in the service of their country," he said.