Five of the six soldiers killed in the deadliest single attack on British forces in Afghanistan since 2001 were aged 21 or under, the Ministry of Defence said on Thursday.

The men, who had reportedly been in the country for less than a month, died when a massive explosion ripped through their armoured vehicle during a patrol on Tuesday near the city of Lashkar Gah in Helmand Province, southern Afghanistan.

Taliban insurgents on Thursday claimed responsibility for the attack, saying they had used a land mine.

The deaths pushed the number of British dead since the 2001 invasion of Afghanistan over the 400-mark, to 404.

The youngest victim was 19-year-old Private Christopher Kershaw while three others were 20 and one was 21.

The five younger victims were from 3rd Battalion The Yorkshire Regiment.

Mourners left flowers outside the battalion's base in Wiltshire, southwest England.

The oldest of the victims was 33-year-old Sergeant Nigel Coupe from 1st Battalion The Duke of Lancaster's Regiment.

The men's Warrior vehicle was hit by an apparent improvised explosive device and burst into flames, reportedly leaving the bodies charred.

It was the greatest British loss of life in Afghanistan since 14 crew were killed when a Nimrod aircraft crashed in 2006. An investigation found the crash was caused by a leaking fuel pipe.

The British defence ministry has not specified the source of the blast and there had been speculation that the explosion was caused by a Soviet-era mine.

But the Taliban said in a statement on their website: "Mujahedeen (holy warriors) of the Islamic emirate have reported that a land mine of mujahedeen blew apart a tank of British invading forces in Greshk district.

"All the invaders on board were incinerated," it added.

Britain has 9,500 troops with the NATO force of some 130,000 in Afghanistan, but Prime Minister David Cameron announced in July that this would be reduced by 500 to around 9,000 this year.