The tough West-based Royal Marines fighting Taliban insurgents on the Afghan frontline will not be deterred by the increasing deaths in their ranks, their former commanding officer has said.

Major General Gordon Messenger says 40 Commando have proved themselves mentally and physically many times and remain focused on their mission.

His comments come as another soldier died from injuries sustained in an explosion in Afghanistan earlier this month.

And last night Chief of the General Staff, General Sir David Richards, said talks with the Taliban should begin "pretty soon" as part of the exit strategy for international forces in Afghanistan – after David Cameron said Britain should seek to leave the war-torn nation by 2015.

However, in the meantime Maj Gen Messenger knows there will be many families in the South West who will be suffering and urged people in the region to support relations of the Taunton-based marines.

Since beginning their six-month tour in April they have suffered 10 fatalities, including four in four days last week.

Maj Gen Messenger led 40 Commando during the Iraq War, when they spearheaded the amphibious assault on the Al Faw peninsula on the first night of hostilities.

He was awarded the Distinguished Service Order in recognition of his outstanding leadership.

And he served as British Commander of Task Force Helmand during the 3 Commando Brigade deployment to Helmand in 2008-09, before being appointed lead spokesman on British operations in Afghanistan.

So there is no one better qualified to assess the morale of the marines during fierce fighting that is claiming the lives of their comrades, and he insists it only strengthens their resolve and determination.

He told the Western Daily Press: "No one is pretending anything other than there is a determined enemy out there that are trying to kill them and do harm to the progress that is being made there.

"But the fact that, in the face of these casualties, they are continuing to go out and engage the population and continuing to reassure the people is to their utmost credit.

"We don't, and frankly we can't, measure success or failure by the number of casualties. Clearly we do everything we can to reduce the number of casualties and this is constantly an evolving operation which looks at the way the enemy are coming at us and changing our tactics, changing our capabilities to best counter them.

"But we are going to take casualties and the sad fact is we are going to continue to take casualties. The guys went to Sangin with their eyes open.

"The guys knew when they went that Sangin was a very, very difficult place. While I certainly do not suggest this is anything but very, very hard graft and occasionally harrowing, they will be utterly focused on the mission ahead.

"If you are a Royal Marine Commando you have already made the case for being considered a pretty special individual.

"To become a Royal Marine Commando you need to show physical fitness but perhaps more importantly mental fortitude as well, and it is exactly those sorts of qualities that will get these guys through this, and ensure that they remain committed to what they know is important."

Maj Gen Messenger, who is married with three children and lives in Somerset, says families play a vital role.

"If it is difficult for the guys on the ground, it is five times harder for the families because they don't experience it, they get it reported back to them," he said. "They aren't with others who are engaged in the same sort of business so it is difficult for them to relate, and while there is an enormous amount of effort that goes into supporting the families we accept that our families pay a price and it is a daily difficulty for them.

"Given that they didn't sign up to be Royal Marines or servicemen it is something I think the nation and the people of the South West need to be very proud of and grateful for."

There is evidence – in the shape of the repatriation ceremonies at Wootton Bassett, support for Help for Heroes and the success of Armed Forces Day at the weekend – that the country does support the troops.

Maj Gen Messenger said: "I think it is getting behind them absolutely, and the families are an important part of this."