United Nations: Syria has told international envoy Kofi Annan in a letter that it is "keen to end violence" but insists that armed opposition groups give up their weapons first.

The Syrian response falls far short of US and European demands that Syrian forces stop fighting first, and even Russia's insistence that both sides lay down their arms simultaneously.

But it does leave the door open for talks, and Annan is sending a team to Damascus on Sunday to continue discussions on implementing his proposal to end the yearlong conflict.

Annan said yesterday that if the team makes sufficient progress he will consider returning to Damascus, where he held two rounds of talks last weekend with President Bashar Assad.

The Syrian letter, obtained on Saturday, asks Annan, the joint UN-Arab League envoy, "to provide guarantees to the Syrian government that the armed groups will cease all armed aggressions and give up their weapons to the dedicated authorities in exchange of a full pardon."

The Syrians said they want the "guarantees" because of "the lessons" they learned dealing with Arab League monitors. The monitors were supposed to ensure Syrian compliance with an Arab League plan that Assad's government agreed to on December 19 calling on Syria to remove heavy weaponry, such as tanks, from all cities, free all political prisoners and allow in human rights organisations and foreign journalists.

But the monitors were withdrawn in late January amid heavy criticism that the Arab League mission had failed to stop the crackdown.

The Syrians said that when the Arab monitors were in the country and they withdrew all their forces from cities and other urban areas "the armed groups used their weapons and attacked the population as well as the public order police and destroyed (the) Syrian economy."

The letter, first reported by the Lebanese newspaper An-Nahar, also demanded from Annan that neighbouring countries control the flow of arms through their borders, and that countries that have called publicly for weapons and financing for armed opposition groups stop doing so.

When Annan provides all these guarantees, "the Syrian government can discuss with him the idea of putting in place a neutral monitoring system," the letter said.

On the humanitarian front, a Syrian-led assessment team with technical experts from the United Nations and the Organisation of Islamic Cooperation is scheduled to start visiting key cities affected by the uprising this weekend.