Mr Brown said British troops were helping improvements
Prime Minister Gordon Brown has urged all Nato countries involved in the war in Afghanistan to make "their fullest possible contribution".
The prime minister paid tribute to UK troops killed in Afghanistan, saying they died serving a "noble cause".
He said Britain was in Afghanistan to stop the Taleban taking over and al-Qaeda returning.
He told MPs the French decision to put in extra forces meant US marines "could move south in Helmand province".
At prime minister's questions there were a series of questions about Afghanistan - where in June more foreign troops were killed than in any month since the fall of the Taleban in 2001.
Mr Brown paid tribute to Lance Corporal James Johnson who died on patrol in Lashkar Gar on Saturday and Warrant Officer Dan Shirley, who died in an accident in Helmand on Friday.
Labour backbencher Jeremy Corbyn asked if the UK's strategy needed re-examining, in the light of continuing deaths and poppy crops.
Mr Brown replied that the number of poppy-free fields had been "doubled" and said Britain was there to stop the Taleban and al-Qaeda returning - something that was a threat, not just to the Afghan people, but to Europe.
But he told MPs that Afghan forces would take over "more and more responsibility" for security as their capability improved.
The Lib Dem MP Bob Russell asked Mr Brown about the lack of European Nato countries in southern Afghanistan and whether it was "time our European allies did more to send their troops to the front line and not rely on Britain to take the brunt".
Mr Brown replied that things were improving as a result of the British troops' presence in Afghanistan and quoted chief of defence staff Jock Stirrup as saying the progress over the past few months had been "remarkable".
But he added: "I agree with him that every country who has signed up to the coalition forces should make a contribution and in some cases a bigger contribution than they are making at the moment."
He said the French had agreed to put extra forces into Afghanistan and the Germans had offered support with policing, while all European countries with helicopters had been asked to make them available.
Tory MP Sir Peter Tapsell asked whether the prime minister's "bleak message to the country" was that for years to come he and his successors would be paying tribute to the soldiers killed in Afghanistan the previous week fighting "an unwinnable and deeply unpopular war".
Mr Brown replied that he was welcome to visit Afghanistan to see the progress that had been made - particularly on education for girls.