Gordon Brown has promised more support for UK troops in Afghanistan, during a surprise visit to the country.
Speaking from Helmand province, he pledged greater protection for troops from roadside bombs, which hours earlier claimed another British life.
His plans, which include the training of another 50,000 Afghan soldiers, came in the wake of criticism that UK forces are under-resourced.
The Conservatives said he was "woefully slow" in properly equipping soldiers.
As the prime minister was flying home from Afghanistan, the Ministry of Defence announced the death of the 208th UK soldier to have died in Afghanistan since 2001.
A Royal Marine was killed on foot patrol in Helmand early on Saturday morning.
On his fourth visit to the country this year, the prime minister said that getting another 50,000 Afghan troops trained by November 2010 would enable them to "take more responsibility for their own affairs".
He said new equipment was being brought in to the field, such as more armoured vehicles.
"[This is] new equipment simply to give better protection to our forces and at the same time to make them more manoeuvrable.
"That - working with a big lift in the Afghan forces - is going to be the next stage of the post-election effort in Afghanistan."
In 40-degree heat in the Helmand capital of Lashkar Gah, Mr Brown viewed the reconstruction work being carried out, and met Air Chief Marshal Sir Jock Stirrup, Chief of the Defence Staff, and US commander General Stanley McChrystal.
In promising greater help to counter the threat of improvised devices - which have caused a heavy toll among British forces - Mr Brown said another 200 extra anti-IED (improvised explosive device) specialists would be deployed in the autumn.
There would also be more unmanned surveillance aircraft and better protected vehicles, he said.
All these measures are to be paid for out of government reserves, over and above the defence budget.
The BBC's deputy political editor, James Landale, who was in Helmand with the prime minister, said that training that number of Afghans so quickly could potentially require an increase in the number of British troops.
There are currently 9,000 UK troops in the country, mostly in Helmand.
Shadow defence secretary Liam Fox said: "IEDs are the single biggest killer of British forces in Afghanistan and this government has been woefully slow to provide our troops with the equipment they need to minimise the risk to them in a very dangerous environment.
"While we welcome this much needed increase in counter-IED capability, the prime minister has left many questions unanswered."
These include, said Mr Fox, what will happen to the extra 900 troops temporarily deployed to provide increased security for the elections, and why so few of the 158 Ridgback protected vehicles ordered two years ago were now on the frontline.
Former commander of British forces in Afghanistan, Colonel Richard Kemp, said increasing Afghan Army numbers from 85,000 to 135,000 in that time frame was possible if the US and UK invested sufficient resources.
"It's essential we get them trained to give us some sort of exit strategy," he said, otherwise there was a danger the mission would lose public support and "drift".
While in the country, the prime minister spoke on the phone with President Hamid Karzai and his leading opponent, Abdullah Abdullah.
British troops had been trying to secure parts of Helmand ahead of the presidential election nine days ago.
The latest results showed President Karzai widening his lead and edging closer to the 50% required to avoid a run-off.
BBC correspondent Chris Morris, in Kabul, said that counting of votes has been slow amid "massive" allegations of fraud directed at the government.
Last week the new head of the British army, General Sir David Richards, pledged to focus on the military effort in Afghanistan, as he took over the role.