David Cameron today urged George Galloway not "to play to the gallery" over the Afghan war.
Mr Galloway, elected Respect MP for Bradford West, last month, returned to the Commons yesterday after a two-year absence.
Called to ask today's final question at the Prime Minister's weekly Westminster grilling, Mr Galloway said: "As I was saying Mr Speaker, there is an iron-clad consensus across the frontbenches about what they now call a 'mission', but given the amount of blood on the ground and rapidly deteriorating military situation most of us call a 'war' in Afghanistan."
Mr Galloway branded the fighting "a bloody maw" and asked Mr Cameron to reconsider Britain's position of withdrawing troops by the end of 2014, following Australian prime minister Julia Gillard's accelerated timetable for pulling out Australian forces.
But Mr Cameron said: "I profoundly disagree with you.
"Our troops are in Afghanistan not fighting a war against Islam but at the invitation of an Islamic government and under a United Nations resolution to try and help that country have a peaceful, prosperous and stable future.
"You know the dangers in the past of walking away from Afghanistan and leaving that country to become the terrorist-supporting haven it did under the Taliban.
"We mustn't make that mistake again and I would urge you not play to the gallery on this issue but to speak up for the work our forces are doing to make Afghanistan a safer country."
Today's session of Prime Minister's questions began with Mr Cameron and Labour leader Ed Miliband paying tribute to the four servicemen killed in Afghanistan since Parliament rose for the Easter recess.
Mr Galloway won a stunning by-election victory in Bradford last month, securing a 10,000-plus majority to oust Labour.
The controversial politician and Celebrity Big Brother star was previously a Labour MP before falling out with the party over wars in Afghanistan and Iraq.