Britain has now lost 184 soldiers in Afghanistan since it joined the US-led invasion in 2001, more than the 179 deaths during its campaign in Iraq that began in 2003.
Fifteen soldiers, including four officers, have been killed in the past 10 days as British and US troops have carried out offensives aimed at pushing Taliban fighters out of Helmand province.
The heavy losses threaten to damage British public support for the deployment in Afghanistan.
David Miliband, the British foreign minister, said that it had been a "grievous few days" in Afghanistan, but that Britain would not be safe until security had been established in the central Asian nation.
"We know that they are engaged in a very, very difficult mission and we have a responsibility to engage the country in understanding that mission and supporting it," he told BBC radio.
"This is about the future of Britain because we know that the badlands of Afghanistan and Pakistan - that border area - have been used to launch terrible attacks, not just on the United States, but on Britain as well.
"We know that until we can ensure there is a modicum of stability and security provided by Afghan forces for their own people, we are not going to be able to be secure in our own country."
Britain has raised force levels to around 9,000 from 8,100 to improve security in the run-up to Afghanistan's presidential election, due to be held on August 20.
The UK ministry of defence said all the latest fatalities occurred in Helmand.
On Friday, five soldiers from the 2nd Battalion The Rifles were killed by two blasts while on foot patrol near Sangin while a soldier from the 2nd Royal Tank Regiment was killed by an explosion during an operation near Nad Ali.
United States: 730
Other nations: 67
A day earlier, a soldier from the 4th Battalion The Rifles died in an explosion while on foot patrol near Nad Ali, while a soldier from the Princess of Wales's Royal Regiment attached to the 1st Battalion Welsh Guards was killed by a bullet wound.
Despite the rising troop toll, Jock Stirrup, Britain's chief of defence staff, insisted that British troops were winning in their mission to improve security in Afghanistan.
"But it's going to take time and alas it does involve casualties ... Our people out there know what they are there to do and they know they are succeeding in it," he said.
Chris Bellamy, a UK-based security analyst, told Al Jazeera: "The British have certainly been knocked back in the last 10 days, but you have to remember that if you go to war you are going to lose people.
"The British and Amercians launched this major offensive three weeks ago and the Taliban know full well that they have to hang on to Helmand," he said.
"It is one of the main poppy growing areas and also its very easy to move across the border from there into Pakistan because the terrain is less difficult than the high mountains to the far east, so the Taliban know they have got to hold it."
Gordon Brown, the British prime minister, said there was no question of pulling soldiers out of Afghanistan until the international community had finished its mission there and quelled the threat from the Taliban.
"This is a very hard summer - it's not over," he said at the G8 summit in Italy.
"But it's vital that the international community sees through its commitments."
Brown said Britain's resolve to complete the work in Afghanistan "is undiminished. We must help deliver a free and fair presidential election in Afghanistan".
The ongoing wave of violence has not been limited to just Afghanistan's south.
In Ghazni, a central province, four security guards were killed in an attack on Saturday, authorities said.
The guards were killed when a supply convoy they were escorting to a Nato-led base came under rocket attack, Kheyal Baz Sherzai, Ghazni's police chief, told the AFP news agency.
A day earlier, in the same province, 11 fighters were killed in an operation by Afghan and international forces, Mohammad Osman Osmani, the governor, told the AFP.
Separately, the Afghan interior ministry announced that 29 fighters were killed in Uruzgan province in the south on Friday.