The US, Europe's three leading powers and Saudi Arabia, Egypt and Jordan will meet in Geneva on Friday to try to revive the so-called Small Group on Syria.
The UN-sponsored effort to end the war in Syria has been overtaken by the Russian-led Astana process over the past 18 months, although neither has ever appeared close to a breakthrough on peace.
Geir Pedersen, the UN Secretary General's special envoy for Syria, confirmed Friday's planned talks during a trip to New York, where he delivered his second briefing to the Security Council after a surge in fighting in the north-western province of Idlib and elsewhere.
This week's meeting in Geneva is the first concrete sign that the UN is trying to unify co-operation on Syria to speed up the search for a political solution.
“I remain convinced that key international players agree on far more than it might seem,” Mr Pedersen said. “All understand the need for international co-operation in Syria.
"I will continue to use my good offices to help the key players with influence to join in one active conversation, to provide common support to a Syrian-led and owned process under UN facilitation.”
The Small Group comprises Britain, Egypt, France, Germany, Jordan, Saudi Arabia and the US.
Friday's session will be followed by a meeting later in May, where Mr Pedersen, again in Geneva, will host the Astana members – Russia, Iran and Turkey.
The UN's main peace effort on Syria fell into disarray as fighting raged and the country's president, Bashar Al Assad, gravitated towards the Astana process led by his main allies in the war, Russia and Iran, and neighbouring Turkey. Those parties met last week.
Unable to contain the conflict, Mr Pedersen's predecessor, Staffan de Mistura, effectively ceded his position to the Russian-led effort.
Since Mr Pedersen last briefed the council in February, he has twice met Syrian Foreign Minister Walid Muallem in Damascus.
He also held two rounds of talks with the opposition Syrian Negotiations Commission in Riyadh and Geneva.
Those discussions are seen as confidence-building measures that could eventually lead to a political settlement capable of ending more than eight years of war in which more than half a million people, mostly civilians, have died and millions more have been displaced.
Agreement could soon be reached on the make-up of a new committee to draft a constitution for post-war Syria, said Mr Pedersen, a Norwegian diplomat.
Forming the constitutional committee would be "a first sign of real movement" towards peace.
Asked if the committee could hold its first meeting this summer, he said: “Yes, I'm hopeful. I believe it should be possible to move forward. We have made tangible progress”.
Mr Pedersen said the need to make advances was urgent because the situation on the ground remained dire.
“We have seen a very troubling surge of violence in recent weeks, in and around the Idlib de-escalation zone” and in other parts of the country, with attacks by and against government forces, he said.
The US ambassador to the UN, Jonathan Cohen, welcomed Friday's meeting in Geneva.
Mr Cohen said the Astana process was failing because Mr Al Assad “seems determined to wage war” while people are starving and aid convoys are stopped from reaching them.
Britain's permanent representative to the UN, Karen Pierce, said there had been reports of government forces on Tuesday morning dropping barrel bombs in northern Hama for the first time in seven months.
Ms Pierce said it seemed to be proof that the Syrian president was not serious about peace.
“This is indiscriminate. Use of indiscriminate weaponry is unacceptable,” she said.
Ms Pierce repeated that Britain and Europe would not consider helping Syria to rebuild without a credible political settlement.