Gordon Brown pledged more troops for Afghanistan today - as the latest British casualties were brought home.
The Prime Minister said the UK military presence would be pushed to its "highest level" of more than 8,000 in order to keep up pressure on the Taliban.
Despite repeated warnings that Britain's armed forces are stretched to the limit, Mr Brown also rejected the idea that there should be a "trade-off" reduction in troops in Iraq.
The announcement came at a joint press conference with George Bush during what is expected to be the US President's last formal visit to London.
The Prime Minister added that the message from the two leaders to the Iranian people was they did not have to choose a "path of confrontation" with the West. Britain wanted to do "everything possible" to maintain dialogue with Tehran, he said. "But we are also clear that if Iran continues to ignore (United Nations) resolutions, to ignore our offers of partnership, we have no choice but to intensify sanctions."
He said Britain would urge Europe to impose "further sanctions" on Iran. Action would be taken to seize the overseas assets of the country's biggest bank and a new phase of sanctions would start on oil and gas.
Both leaders paid tribute to five UK soldiers killed over the past week, whose bodies arrived back at RAF Lyneham in Wiltshire this afternoon.
But despite the British death toll from the campaign hitting 102, they reiterated their belief that the insurgents still had to be tackled "or Afghanistan would come to us".
Mr Bush admitted that the situation in Afghanistan was "tough work", but insisted that the "march to democracy is never smooth".
"I believe it's necessary work in the interests of peace and security," he added.
Mr Bush also ought to play down persistent rumours of a rift between the two men over the UK's plans for drawing down troops in Iraq. The US does not view the security situation as robust enough for levels to be reduced yet.
Mr Bush lavished praise for being "tough on terrorism", and stressed that Mr Brown had left higher numbers in Basra province than "initially anticipated".
"The first thing about Gordon Brown, he is tough on terrorism, and I appreciate it," Mr Bush told journalists in the Foreign Office. "So should the British people... You have been strong on Afghanistan and Iraq and I appreciate that. But more importantly, the people of Afghanistan and Iraq appreciate it."
The Prime Minister said UK troops were moving from a combat to an "overwatch" role in Iraq, but added that he would not impose an "artificial timetable" on withdrawal.
"You cannot trade numbers between the two countries," he said. "In Iraq there is a job to be done and we will continue to do the job, and there is going to be no artificial timetable. And the reason is that we are making progress."
He also thanked Mr Bush for his "steadfastness and resolution" in rooting out terrorism around the world.
Defence Secretary Des Browne is due to give details of extra specialist troops being sent to Afghanistan in a statement to the Commons this afternoon.
Up to 300 engineers, logistical staff and military training experts are expected to begin a tour of duty over the next few weeks.
The announcement will bring the overall UK strength in Afghanistan to more than 8,000 - mostly based in the volatile Helmand province.
Tensions have been rising in the south of the country, with President Hamid Karzai warning he will send troops into Pakistan if Islamabad does not prevent cross-border attacks by the Taliban.
The British casualties repatriated today were all from 2nd Battalion, the Parachute Regiment, based at Colchester, in Essex.
Privates Nathan Cuthbertson and David Murray, both 19, and Daniel Gamble, 22, were blown up by a suicide bomber last Sunday.
And on Thursday, Lance Corporal James Bateman, 29, and Private Jeff Doherty, 20, were killed when they came under Taliban fire.
The Liberal Democrat defence spokesman Nick Harvey said: "Further support for the vital work our troops are doing in Afghanistan is welcome. However, the Government is still failing to address the pressing issue of overstretch in our armed forces.
"It is becoming increasingly clear that our troops are being kept in Iraq largely for the political convenience of President Bush.
"It is time the Government set a timetable for withdrawal of our forces from Iraq. By continuing to try to fight on two fronts, we are endangering our chance to build lasting security in Afghanistan."
Scottish National Party defence spokesman Angus Robertson said today's announcement was "obviously an escalation in our military commitments" and called for a parliamentary vote on any further deployment.
Mr Robertson said: "If this deployment gives short term security relief then so be it, but we need the Government to resist a further escalation of our military commitments.
"There are very real difficulties faced by servicemen and women as well as their families by the ongoing overstretch and regular breaches of the harmony guidelines, which are supposed to guarantee sufficient time at home between deployments.
"Gordon Brown should not be allowed to put more of our brave troops in harm's way without specific new authorisation from Parliament."Reuse content