International attention has turned toward forming a broad-based government in Kabul to head off feared ethnic clashes.
Mr Lakhdar Brahimi, the UN envoy for Afghanistan, said UN political personnel had been asked to go to Kabul immediately.
Mr Brahimi said there were three choices, the best of which was an "all-Afghan" security force. If this were not possible, he proposed a multinational force, which diplomats said could include Muslim troops from Turkey and Jordan as well as European forces.
The third and worst choice he said was a traditional UN peacekeeping force, which would take months to organize.
Alliance Foreign Minister Abdullah Abdullah said his fighters had only entered Kabul to maintain security. He welcomed UN involvement and called on all Afghan groups to come to Kabul to discuss a future administration, adding, "Taliban excluded."
He also promised to hold democratic elections in Afghanistan within the next two years.
However, the US has insisted on a government containing moderate members of the Pashtun ethnic grouping, form which the Taliban received the majority of their support.
In Rome, a senior adviser to Afghanistan's exiled former King Zahir Shah, seen as a key player in the country's political future, said the Northern Alliance had broken an agreement by entering Kabul but an Alliance spokesman called on Zahir Shah to send a delegation for talks on a new government.
Pakistani President Pervez Musharraf said a UN force with Muslim participation was needed urgently to ensure Afghan stability and Turkish Foreign Minister Mr Ismail Cem said Turkey, NATO's only Muslim member, was willing to send peacekeeping troops but must have a say in planning the country's future.