British, Afghan and coalition forces captured four key Taliban strongholds in southern Afghanistan during a massive operation that saw them fight at close quarters, knee-deep in mud, it emerged Sunday.

Britain''s Ministry of Defence released details of the operation, which was fought over 18 days around the town of Nad-e-Ali in Helmand province and left five members of the British forces and around 100 Taliban fighters dead.

More than 1,500 troops were involved, making it one of the largest operations mounted by the Royal Marines since the US-led invasion of Iraq in 2003. It culminated in a battle on December 25, Christmas Day.

"Almost every day we were involved in intense firefights ranging from rocket-propelled grenades and small arms ''shoot-and-scoots'' to four-hour battles with the enemy forces as close as 30 metres," said Captain David Glendenning, commander of the marines'' artillery support team.

Some of the marines had to trudge more than 60 kilometres (40 miles) through mud while fighting insurgents, the defence ministry said.

One soldier, a lance corporal and signaller with the 77th Armoured Engineer Squadron, said: "I was in Nad-e-Ali for just over two weeks... Some of the places we stayed in were a nightmare -- sleeping in the mud was the worst.

"(At times) we were exposed and moving ahead of our infantry protection. It felt like we were being watched and it was difficult to tell who the enemy was -- it was pretty scary."