David Cameron has said "we cannot afford to fail" in Afghanistan, warning of serious consequences for Britain and the world if that were to happen.
David Cameron last visited Afghanistan a year ago
He praised the "incredible work" of British troops, but said more needed to be done by Britain's Nato allies.
And he called for "gritty, hard-headed decisions" on how the international community operates in Afghanistan.
The Conservative leader was speaking during a two day trip, a year after his last visit to the country.
He said that Afghanistan under the Taleban had been the "cradle of the terrorism that hit the world on 9/11".
Failing in Afghanistan would have serious consequences for Britain and the rest of the world in terms of terrorism and drugs.
He said: "We do need to say look, the consequences of failure here would be very serious and there are some things that need to change.
"For instance, I think it is now time to look at the idea of having one single individual who could coordinate some of the civilian response in terms of the EU and in terms of the UN, we need better coordination.
"We need to look at how we're working together with our Nato allies and with the Americans, to make sure there's more unity in our command and in our purpose, and we also do need other, Nato countries to do more.
"Britain is definitely bearing its share of the burden, but we need more helicopters, we need more support, and also we need other Nato countries to play their part."
On Wednesday Mr Cameron met the commander of Nato forces in the country, US General Dan McNeill, and the British ambassador Sir Sherard Cowper Coles.
He is also expected to visit British troops fighting the Taleban in southern Afghanistan to show support for their efforts.
He will also be assessing progress of the reconstruction projects which Britain is helping with.
His trip comes a week after Foreign Secretary David Miliband visited Afghanistan and Pakistan.
Mr Cameron's plan to also include Pakistan was dropped because of concerns about security, his aides said.
It also comes a week after Mr Cameron visited Rwanda to announce the Tories' global poverty plan.
He was widely criticised for that trip which coincided with severe flooding in his constituency and other parts of England.
That trip, added to an opinion poll "bounce" for new prime minister Gordon Brown and a row about abandoning support for selection by ability, has led to some criticism of his leadership within his party.
But he dismissed those critics on Tuesday and said Gordon Brown's opinion polls "honeymoon" would not last.