Syria will fall apart if its government and rebels keep fighting instead of seeking a negotiated peace, United Nations Secretary-General Ban Ki-moon has said.
He said the situation in Syria was deteriorating by the day after almost two years of conflict in which 70,000 people have died, but there was now a slim chance for peace talks.
"This is a very small window of opportunity which we strongly support and encourage them to use that. The opportunity may soon close," Mr Ban said at a news conference in Geneva.
Syria's government has shown increased willingness to hold talks with the opposition to end a war that has driven nearly 1 million Syrians to flee their country.
Foreign Minister Walid al-Moualem said on Monday the government would even speak to armed rebels.
On Thursday it extended passport terms for Syrian nationals abroad, meeting a condition set by the opposition for talks.
Delivering an annual lecture in Geneva todau, the UN chief said: "I continue to urge the Syrian parties to find their way to the negotiating table.
"The horrors of the last months and years prove beyond doubt: the military solution in Syria is leading to the dissolution of Syria."
"The Security Council must no longer stand as a silent witness to the slaughter.
"At long last, it must come together and establish the parameters for the democratic transition that might be the last best hope for saving Syria," he said.
Russia insists Assad exit must not be precondition
Russia has blocked UN Security Council resolutions aimed at forcing an end to the conflict and insists the exit of President Bashar al-Assad from power must not be a precondition for a negotiated solution.
On Thursday, Russian President Vladimir Putin cautiously welcomed a suggestion from French leader Francois Hollande that dialogue on Syria be broadened to bring in parties that could act as negotiators between Mr Assad and opposition rebels.
"I am urging again the Security Council and regional leaders and the people of Syria to unite themselves to address this issue," Mr Ban told reporters.
"In just about two weeks time, we will be entering the third year of this crisis. How long (do) we have to see the people killed and displaced in this way?"
He said he would meet his Syria envoy Lakhdar Brahimi at an Alpine retreat in Switzerland on Saturday for private talks along with senior aides.
"There's not much political space... I cannot give you any guarantee or a deadline or any future meetings," he said.
For now, in the absence of a political resolution, humanitarian assistance must be increased, he added.
Meanwhile, the secretary general also said talks should be held as soon as possible on deploying a United Nations peacekeeping force in Mali, where French-led forces are pursuing Islamist rebels ousted from cities in the north.
"The idea of deploying United Nations peacekeeping operations, transforming this African-led support mission in Mali, AFISMA, is now being seriously discussed," Mr Ban said.