Gordon Brown hailed British troops fighting the Taliban as the true heroes of the Olympic year today.

The Prime Minister spent 90 minutes meeting and talking to troops at Camp Bastion - the main UK base in Afghanistan - during a stopover on his way to the Games in Beijing.

But he was unable to escape his domestic troubles. During a joint press conference in Kabul with President Karzai he faced repeated questions over whether his own position was under threat.

In a speech to some 300 troops from 16 Air Assault Brigade, Mr Brown - dressed in a collar and tie but no jacket - said that the nation owed them a "huge debt of gratitude".

"You know that you are in the frontline in the fight against the Taliban. You know that by what you are doing here you prevent terrorism coming to the streets of Britain," he declared.

"This week we are celebrating the Olympics where we have had great success.

"But this week also I believe that our Olympic athletes and everybody else in our country will remember that you have showed exactly the same courage, professionalism and dedication.

"You make our country proud every day of the week and every week of the year. You are truly the heroes of our country."

Mr Brown paid tribute to Corporal Barry Dempsey of the Royal Highland Fusiliers who became the latest British casualty of the conflict when he was killed by an explosion when he left his vehicle.

He also visited the base's field hospital where he met two soldiers who had been seriously wounded by sniper fire.

The dangers were underlined by the death this week of 10 French troops in a Taliban ambush just 30 miles from Kabul in what had been thought to be one of the safer parts of the country.

But despite the grim reminders of the precarious security situation, Mr Brown said that he had been assured by the brigade's commanding office Brigadier Mark Carleton-Smith that morale was high and that they were continuing to make "substantial progress" against the Talkiban.

At his news conference with Mr Karzai, Mr Brown declared his continuing support for the Afghan government.

"We are truly resolute in our determination to support this new democracy of Afghanistan," he said.

"We will not relax our efforts to support the reconstruction of Afghanistan because we understand that what happens in Afghanistan affects the rest of the world."

He announced 120 million US dollars (£64,000,000) in additional development assistance, including funding to pay teachers' salaries - and a further 17 million US dollars (£9,000,000) for radio provisions in Helmand province countering Taliban propaganda.

He also promised further assistance in training and mentoring the Afghan police and army as well as help through the National Civil Service College in establishing a new Afghan civil service.

He suggested that the army - currently 60,000 strong - may have to expand beyond its planned strength of 120,000 in order to meet the security needs of the country.

However, to his obvious irritation, the news conference was dominated by questions from British reporters about his political plight at home and a possible leadership challenge by Foreign Secretary David Miliband.

The Prime Minister insisted that he was concentrating on Britain's economic difficulties and that he had a "good relationship" with Mr Miliband.

"We get on with the job. What people want us to do is get on with the economic problems that face our country and all countries," he said.

"I am getting on with the job and that is what people expect us to do."

President Karzai even stepped in to try to ease the mood, joking: "Cabinet ministers plotting is nothing new. We have it in Afghanistan too."