The United States on Wednesday urged Russia to use its leverage over Syrian President Bashar al-Assad to end the war as the UN envoy warned of a "worrying and dangerous" moment in the nearly seven-year conflict.
"Russia can push the regime to commit to seeking a real peace in Syria," US Ambassador Nikki Haley told a Security Council meeting on the worsening crisis in Syria.
"Now is the time for Russia to use that leverage," she said, to "push the Assad regime to do what it plainly does not want to do."
Following a confrontation between Israel and Iran, clashes involving US-led coalition forces and fighting escalating in many parts of the country, UN envoy Staffan de Mistura called for de-escalation.
"This is as violent and worrying and dangerous a moment as any that I have seen in my time as special envoy," said De Mistura, who has been the peace mediator since 2014.
Next month the war in Syria will enter its eighth year with diplomatic efforts stalled as violence rages on the ground.
Russia's 2015 intervention in the war succeeded in turning the tide in Assad's favor but Moscow's push for a peace settlement, including a high-profile congress in Sochi last month, has yet to yield results.
With so many battlefronts involving forces from several countries, French Ambassador Francois Delattre said "potential for an enlargement of the conflict and a major regional and international confrontation should be taken very seriously."
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More than 340,000 people have been killed in the war, millions have been driven from their homes and 13 million Syrians are in need of urgent humanitarian aid.
Russian Ambassador Vassily Nebenzia complained that "something is being constantly demanded of the Russian Federation" and countered that the United States and its allies should use their influence to ease violence.
A US-led coalition strike against pro-regime forces in Syria in the eastern province of Deir Ezzor last week was an "unprovoked attack," Nebenzia told the council.
Haley earlier said that the coalition had acted in self-defense in the attack that left scores dead.
The council is considering a draft resolution presented by Sweden and Kuwait that would demand a 30-day ceasefire in Syria to allow for deliveries of humanitarian aid to civilians and lift sieges.
Negotiations were continuing Wednesday on the text and diplomats said it remained unclear when the measure could come up for a vote at the council.
Nebenzia told the council that the humanitarian situation was "complex," later telling reporters that a ceasefire could not happen "overnight."
A first aid convoy was allowed into the rebel enclave of Eastern Ghouta on Wednesday after an intense bombing campaign that killed more than 250 civilians.
"We are striving for consensus," Nebenzia said about negotiations on the draft resolution.