Russia and China on Monday vetoed a UN Security Council resolution calling for a seven-day ceasefire in the embattled Syrian city of Aleppo.
Venezuela also voted against the text, while Angola abstained. The 11 other member nations on the council cast their votes for the text.
The vote marked the sixth time that Russia blocked a council resolution on Syria since the conflict began in March 2011, and the fifth time that China did so.
The last time Russia vetoed a Security Council resolution on Syria was in October, when it vetoed a UN draft resolution demanding an end to the bombing of Aleppo.
Moscow, a close ally of Syrian President Bashar Al-Assad, had expressed strong reservations about the text it vetoed on Monday, which was the subject of weeks of negotiations.
In an eleventh-hour effort, Russia tried to postpone the vote until at least Tuesday, when a meeting was set to take place in Geneva between the Americans and the Russians.
But Paris, London and Washington -- the main backers of the text – decided to go ahead anyway.
Russia says the Geneva talks concern a plan for all rebel fighters to withdraw from eastern Aleppo, under siege by the regime. But the rebels have rejected the plan.
The two sides "are close to an agreement on the basic elements," said Russia's ambassador to the UN, Vitaly Churkin.
But deputy U.S. envoy Michele Sison suggested there was no deal, accusing Churkin of using a "made-up alibi."
"We will not let Russia string along the Security Council," she added.
"We will continue bilateral negotiations (with Russia) to relieve the suffering in Aleppo, but we have not reached a breakthrough because Russia wants to keep its military gains."
Had the resolution been adopted, it would have been a "fragile glimpse of hope" and allowed to "save lives," French ambassador Francois Delattre said.
He accused Russia of having "decided to take Aleppo regardless of the human cost" of a military victory.
The draft text demanded that "all parties to the Syrian conflict shall cease... any and all attacks in the city of Aleppo."
It also demanded that the parties "allow urgent humanitarian needs to be addressed," meaning permitting emergency services to enter and serve tens of thousands of residents in the besieged areas.
The temporary ceasefire aimed to pave the way for a cessation of hostilities across Syria, though that would not apply to military operations targeting "terrorist groups" such as the Islamic State (ISIS) group or ex-Al-Qaeda affiliate Fateh al-Sham Front, previously known as Al-Nusra.
AFP contributed to this report.