Gordon Brown has insisted Britain's strategy in Afghanistan is succeeding, despite the bloody fighting which has seen the loss of eight soldiers in 24 hours.
The Prime Minister acknowledged said that the past ten days had been "extraordinarily difficult" for British forces with the deaths of 15 troops since the start of the month.
But in a letter to the senior MPs on the Commons Liaison Committee, he said the Operation Panther's Claw offensive to clear the Taliban from central Helmand was succeeding.
"Despite the tragic losses, morale remains high - and I can report the assessment of commanders on the ground: that the current operations are succeeding in their objectives," he said. "They are having a marked impact on the Taliban in central Helmand, will improve security for the population in the run up to the elections, and will allow longer term work on governance and development to begin."
In his letter, Mr Brown - who is due to give evidence to the committee next week - acknowledged that the losses of recent days had led to questions over whether Britain could succeed in Afghanistan.
But he said that it was essential that the international coalition saw through its commitment if it was to deny al Qaida a fresh foothold in the country from which they could mount terrorist attacks on the West.
"While I know there are some who have questioned our strategy, I continue to believe our strategy is the right one," he said. "It has been a very difficult summer and it is not over. But if we are to deny Helmand to the Taliban in the long term; if we are to help Afghanistan and Pakistan to defeat this vicious insurgency and prevent the return of al Qaida - then it is vital that the international community sees its commitment through."
The latest casualties took the total number of British personnel to have died on operations in Afghanistan since 2001 to 184, surpassing the 179 who died in Iraq.
They included five British soldiers from the 2nd Battalion The Rifles who died in two separate blasts on the same patrol near Sangin, and another British soldier from the 2nd Royal Tank Regiment who died near Nad-e-Ali.
On Thursday two soldiers, one from 4th Battalion The Rifles and the other from Princess of Wales's Royal Regiment attached to 1st Battalion Welsh Guards, were killed in separate incidents.