William Hague has said he would be "very surprised" if Afghan forces did not have responsibility for their own security by 2014.
The foreign secretary insisted there was no timetable for withdrawing troops amid reports of splits among senior Tories about how long they would stay.
But he said he did not expect UK combat forces to still be there by the time of the next general election in 2015.
The UK has about 9,500 troops there, the second largest international force.
Mr Hague made his comments ahead of a major speech in London - his first since becoming foreign secretary in May - in which he set out his vision for a more "focused and effective" foreign policy.
Setting out plans to deepen economic and diplomatic links with countries such as China, India and Brazil, he said the UK must have more "global reach and influence" or face decline in a fast-changing world.
He also called for the UK to have more representation at all levels of the European Commission, arguing that the last Labour government had let British influence in Brussels diminish - an accusation denied by former ministers.
US General David Petraeus - who is now leading Nato in Afghanistan - has said the Taliban insurgents no longer have the momentum.
Separately, the Taliban have told the BBC they have ruled out talks with international forces.
Prime Minister David Cameron said last week that UK forces would not remain in Afghanistan for a "day longer" than it takes to ensure the country's government can handle its own security, adding that he wanted troops out by 2015.
However, Defence Secretary Liam Fox predicted on Wednesday that British forces could be among the last to leave Afghanistan and "strategic patience" was required.
He urged the UK and its Nato allies to "hold our nerve" and show the resolve to "see the job through".
Premature withdrawal would be a "shot in the arm" to violent Islamic extremists around the world and a "betrayal" of the sacrifices made by British forces, he warned.
Following the comments, Downing Street denied there were any differences between Mr Cameron and Dr Fox.
In an interview, Mr Hague told the BBC: "We are committed to the Afghans being able to conduct their military operations and security and that takes time. But I would be very surprised if that took longer than 2014."
He said: "Of course, in the next parliament he would hope - anyone would hope - that the British combat troops were coming home. But [Mr Cameron] has also stressed that's not setting a timetable for what happens over the next few years."
Mr Hague went on: "We have always said... that the Afghan forces should be able to conduct their own affairs, should be able to stand up for themselves without other nations having to be alongside them, by 2014."
The foreign secretary said plans to hand over control by then were "on schedule".
He warned that the public should be "braced" for an increase in casualties in the coming months due the intense nature of the military activity, but argued this should be seen in the context of the fact that Nato forces were "making progress".
The foreign secretary's comments come after the 309th UK military death in Afghanistan was announced.
A senior British officer has also revealed that Taliban insurgents in Afghanistan are smuggling in components for roadside bombs from Iran and Pakistan.
Major General Gordon Messenger added that the threat faced from these devices was "unprecedented in scale".
BBC world affairs editor John Simpson said the Taliban had told him there was "no question of their entering into any kind of negotiations with Nato forces" and that their forces had the "upper hand".
But Mr Hague said: "The Taliban has many different forms. So I don't think there's a spokesman who represents what one might call the Taliban."
He added: "The military pressure on the Taliban will increase in the in the coming months.... [Nato] must overcome the possibility of failure."
Former Liberal Democrat leader Sir Menzies Campbell - now a backbench coalition MP - suggested there were divisions among the Conservative leadership and that "singing from the same hymn sheet would be a good idea".
He added that other recent comments from Dr Fox, calling Afghanistan a "13th Century state", had not been helpful.
On withdrawing troops, Sir Menzies said: "We need something more specific than we have got at the moment.
"We need military success and then we can talk about the political circumstances, and when withdrawal will become possible."
Shadow foreign secretary David Miliband accused Mr Hague of "playing politics" with his speech.
"The idea of him lecturing the Labour Party about joined-up government, when the defence secretary and prime minister can't go more than two days without disagreeing about our most important foreign policy objective, is risible," he said.