The terrain is rough, and vast

But the troops did seize a "great deal" of papers, maps and radios, now being studied for intelligence information.

Operation Ptarmigan was tasked with destroying al-Qaeda bunkers and cave complexes in the mountains to the south east of Gardez.

The area, known as Ginger Valley, was targeted by American troops in Operation Anaconda last month - an offensive in which the US said eight of its own and "hundreds" of the enemy were killed.

It is littered with landmines and the debris of war, including the wreckage of a downed American Chinook helicopter.

Click here to see the marines' kit

Brigadier Lane said this was a "real operation" aimed at destroying any residual al-Qaeda or Taleban forces and denying them future use of any facilities in the region.

The task force discovered a number of previously unknown cave complexes, one of which contained over 20,000 rounds of anti-aircraft artillery ammunition, which was destroyed.

At a press briefing Brigadier Lane said Operation Ptarmigan had achieved all of his initial operation deployment objectives.

"Royal Marines have been operating very effectively at altitudes of up to 11,000ft and in adverse weather conditions.

"This is a tribute to the effectiveness of their training and fitness regime and also the efforts that have been made since arriving in theatre to get used to the local conditions."

Lieutenant Colonel Tim Chicken, who commands W and Z company's of 45 commando, said there were signs some rebel fighters had returned to the area since Anaconda.

He said: "Whilst we did not come across any Taleban or al-Qaeda there was evidence and indications that the facilities had been used."

Harsh conditions

"So, I would take it from that that the whole area remains one of some danger."

However, at least one marine was disappointed he had not confronted the enemy so far.

"It would be a shame to come all this way and not have any contact - all the lads have trained for it," said Andrew Robertson, 24, from Glasgow.

BBC correspondent Jonathan Charles spent 24 hours in the combat zone with the troops, and described the harsh conditions the marines were dealing with.

He said: "It's very tough up there, no doubt about it. They're operating at 10,000ft above sea level which makes breathing very difficult."

He said the 63kg (138lb) flak jackets and packs the men were carrying posed another problem, as did the landmines, the rough terrain and freezing temperatures.

Meanwhile, more than 100 extra Royal Marines are due to arrive in Afghanistan.