The deaths of three more soldiers in Helmand province demonstrate the ferocity of the war of attrition that has erupted in the run-up to the Afghan presidential election on Thursday.

Thirteen British soldiers have been killed so far this month, and 22 died last month. In June, before the Operation Panther’s Claw offensive was launched to drive the Taleban out of central Helmand in preparation for election day, four soldiers were killed.

The Taleban have vowed to disrupt the voting and have laid minefields of improvised explosive devices (IEDs) to target both British and Afghan troops and civilians.

On Saturday the milestone figure of 200 British deaths was recorded when it was disclosed that a soldier from the 2nd Battalion The Royal Welsh had died of his wounds while being treated at the Royal Centre for Defence Medicine in Selly Oak, Birmingham. His vehicle had been hit by an IED near Musa Qala, northern Helmand, on Thursday.

Within 24 hours the Ministry of Defence announced that another soldier had been killed by an IED. The 201st British soldier to die in Afghanistan, from the 2nd Battalion The Royal Regiment of Fusiliers, had been on a foot patrol near Sangin, south of Musa Qala. Then last night, the MoD announced that three more had been killed.

The sharply rising number of dead and seriously wounded is putting huge pressure on commanders.

Of the 204 soldiers who have died, 66 have been killed this year, which compares with 51 for the whole of 2008, 42 in 2007 and 39 in 2006. The MoD is to release figures today for the number of personnel wounded in July, and it is expected that the total could be close to 100, double the number injured in battle in June. Senior officers in Helmand, where 6,200 of Britain’s 9,140 troops in Afghanistan are based, insisted, however, that the landmark of 200 deaths would not deter them from their mission.

Lieutenant-Colonel Nick Richardson, spokesman for Task Force Helmand, said that morale remained high. Speaking from the British headquarters at Lashkar Gah, he said of the British force: “They’re undaunted. Their resolve and determination is only hardened by the challenges we face.”

However, with so many soldiers being wounded in the IED attacks, of which there are at least three or four for every soldier killed, the attrition rate is taking its toll. Already a company of 125 soldiers has had to be sent from the 3rd Battalion The Yorkshire Regiment, a reserve force in Cyprus, as replacements for casualties.

A team of army officers reporting to General Sir Richard Dannatt, the Chief of the General Staff, acknowledged in a confidential document that the pressure on the Service was “compounded by the impact of undermanning, injury and wounding”. The document, dated April 2009, leaked to The Sunday Telegraph, said that commanders were increasingly worried they were being asked “to do too much with too few resources”.

In the report, General Dannatt, who retires on August 28, admitted that progress in Afghanistan had been slow and that operational demands would remain high for the foreseeable future.

Gordon Brown pledged to push ahead with the mission. He described the latest deaths as “deeply tragic”.

“In these moments of sorrow and sadness, we must never forget why we are in Afghanistan and why people are making the sacrifice that they are making,” the Prime Minister said. “Three quarters of the terrorist plots that hit Britain derive from the mountain areas of Pakistan and Afghanistan and it is to make Britain safe and the rest of the world safe that we must make sure we honour our commitment to maintain a stable Afghanistan.”

British troops have been in Afghanistan eight years, and this year is proving the bloodiest. The death toll in Afghanistan is nearing the number of British combat deaths in the 1982 Falklands conflict — 255. But that was a short war that ended with a clear victory.

The three soldiers who died on Friday in Helmand and were named by the MoD over the weekend had all been taking part in protecting a shura (meeting) between British officers and elders in preparation for the presidential election.

Lance Bombardier Matthew Hatton, 23, of 40th Regiment Royal Artillery, was wounded in the initial attack in Sangin on Thursday.

Captain Mark Hale, 42, and Rifleman Daniel Wild, 19, both from the 2nd Battalion The Rifles, were carrying him to a helicopter landing zone when there was a second explosion, killing Lance Bombardier Hatton and Rifleman Wild. Captain Hale died of his injuries later in hospital.

British Forces in Afghanistan will mark the deaths of the latest soldiers killed in the campaign in the same way they remember all their fallen comrades. Flags will be lowered to half-mast at every British base in Helmand and remembrance services will be held when their bodies are repatriated.

The governor of Helmand province paid tribute to the sacrifices made by British troops in his country. Gulab Mangal said he believed that their courage would result in “a better Afghanistan and a safer world”.

“Once again, we in Helmand have sad cause to remember the debt we owe to the men and women of the British Army and the people of the United Kingdom,” he said.

“The lives of all your brave soldiers are precious to us and we grieve at your loss. We are grateful beyond words for the sacrifices you make on our behalf. You deliver us from the enemies of peace, and you give us hope that our future will be free from the fear, suffering and oppression of our past.

“I believe with all my heart that the legacy of your courage will be a better Afghanistan and a safer world.”

- A former soldier employed by a security company has been killed in Herat, western Afghanistan. The man, from Ballykelly, Co Londonderry, was reported to have died in an ambush. It is understood that he was employed by the London-based ArmorGroup International.

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