Rahim and Brahimi: More smiles than substance?
But the country's interim Defence Minister, General Mohammad Fahim, earlier said that he thought the force should be limited to only 1,000 soldiers, whose role would be to guard government buildings.
For his part, Mr Brahimi said he had not discussed operational details during his talks.
Mr Brahimi had earlier held talks with new Foreign Minister Abdullah Abdullah, as well as Mr Fahim and outgoing President Burhanuddin Rabbani.
However, he was unable to meet the head of the interim administration, Hamid Karzai, who remains in Kandahar, following last week's surrender of the Taleban authorities there.
The UN office in Kabul said Mr Brahimi might still meet Mr Karzai on Wednesday, before the UN official flies to Pakistan for talks with President Pervez Musharraf.
British role
At the Bonn peace talks, a pledge was made to demilitarise Kabul before the deployment of UN-mandated peacekeepers, but on Monday the Northern Alliance insisted that it would not withdraw all of its troops from the city.
UK Prime Minister Tony Blair has said Britain is willing "in principle" to play a leading role in establishing a peacekeeping force for Afghanistan.
Speaking following talks with US Secretary of State Colin Powell in London on Tuesday, Mr Blair said decisions on the deployment of a force would have to be made "relatively quickly".
But he said there was still "an immense amount of details to be decided and discussions to be had" before any force was put in place.
Voices of dissent
The issue of peacekeeping troops is just one of the problems facing Afghanistan's new government.
It is due to take office on 22 December, but there has already been serious division over the allocation of power.
The dissent has focussed on the allocation of all of the three key ministries - defence, foreign and interior - to members of Mr Rabbani's Jamiat-e-Islami party.
The three ministries went to men from the Panjshir Valley, the stronghold of slain Northern Alliance commander Ahmed Shah Massoud, who was assassinated on 9 September.
But Mr Brahimi said after his talks in Kabul that the transition on track.
"The three key ministries haven't just been given to one party in the alliance, but to one district of Panjshir. This is unfair," said Rashid Dostum, an alliance warlord who controls Mazar-e-Sharif in northern Afghanistan.
It had been feared that Mr Dostum would block the new government because of his objections, but the UN says it has been reassured that this will not happen.
In a message to the UN's special representative to Afghanistan, Lakhdar Brahimi, Mr Dostum, who controls large areas of the north of the country, said he would not support any efforts to derail the power-sharing deal reached in Bonn.