British troops could remain in Afghanistan for at least 15 years to shore up domestic security, the country's president said today.
Speaking ahead of the London conference, Hamid Karzai explained that enough police and soldiers could be trained and equipped within five to 10 years, but "sustaining" them would take longer.
Prime Minister Gordon Brown told the BBC Radio 4 Today programme that the number of troops and police officers would rise to 300,000 by 2011, and the number of British troops in the country could be gradually reduced.
But Mr Karzai said: "With regard to training and equipping the Afghan security forces, five to 10 years would be sufficient. With regard to sustaining them... the time period extends to 10 to 15 years."
Mr Brown would not be drawn on a timetable, and said instead that British withdrawal depended on conditions in the country.
He said: "I'm not giving a timescale; what I'm saying is, if the conditions are met, that security can be taken over by the Afghans in the provinces in which we operate, then British forces will not be needed at the level they are at the moment."
Mr Karzai told the programme that the leaders expect to emerge from the conference with a "clear agenda" for the next five years, and said Afghanistan would try its best to meet its end of the security bargain.
He said: "We will try our best to deliver. There are expectations in Afghanistan too. The Afghan people want a better future, a more secure future.
"It's absolutely in the best interests of Afghanistan that we train an adequate number of troops and train them properly and Afghanistan must provide the men which we will do."
Mr Brown said that, as well as strengthening Afghan security, non-violent elements of the Taliban would be persuaded to take part in the "democratic process".
He said: "We are looking at a group of people who are easily divided because most of them have got different reasons for being part of this insurgency. Some are ideologically committed and support al Qaida and they have got to be driven out and dealt with."
But he said the rest included factions such as mercenaries who may be persuaded to back the country's government and renounce violence.
The Prime Minister also stressed that Britain's presence in the country is necessary to protect the UK from terrorist plotters.
He said: "Three-quarters of the terrorist plots until now that we have had to deal with don't emanate from London or Europe or any other part of the world, they emanate from the Afghanistan-Pakistan border.
"It's about the safety and security of our citizens, and 43 nations are involved in this because they are worried also."