Also on Monday, a British fighter jet crashed injuring its two pilots. A day earlier, in an unrelated incident, a British soldier was killed in a bomb attack, bringing to 17 the number of British troops killed in July.
The death toll is likely to increase political debate in London over the UK's role in the conflict.
Jaap de Hoop Scheffer, the outgoing Nato chief, who is in London for talks with Gordon Brown, Britain's prime minister, called the recent deaths in Afghanistan "tragic" and said it was right that there was debate.
But he warned: "If we were to walk away, Afghanistan would fall to the Taliban, with devastating effect for the people there - women in particular.
"Pakistan would suffer the consequences, with all that that implies for international security. Central Asia would see extremism spread. Al-Qaeda would have a free run again and their terrorist ambitions are global."
Separately, the US has suggested it could overhaul its Bagram prison in Afghanistan in a bid to stem alleged abuses there.
Marine Major General Douglas Stone, credited with revamping US detention practices in Iraq, was assigned to assess all detainee issues in Afghanistan, and his recommendations are now being reviewed by Admiral Michael Mullen,, the top US military officer, and Robert Gates, the US defence secretary.
Lieutenant Colonel Alayne Conway, a spokeswoman for the joint chiefs of staff, said no hard dates had been set for completion of the review.