Russian Foreign Minister Sergey Lavrov has said the talks between the Syrian government and opposition groups should start by the end of January as planned, but the invitation list remains a sticking point.
Lavrov met on Wednesday with US Secretary of State John Kerry in Switzerland to bridge the divide, but failed to find agreement.
"We have provided our proposal, the US did the same, and now the members of the Syria opposition groups also provided their proposal" on the invitation list, Lavrov told reporters.
He stressed that it was now up to UN Syria envoy Staffan de Mistura to come up with a solution.
Contrary to the position held by Washington, Lavrov reiterated that the armed groups Jaish al-Islam and Ahrar al-Sham are not acceptable as invitees, labelling them "terrorist organisations".
But despite the failure to agree on the invitation list, Lavrov said neither he nor Kerry had thought about postponing the talks, which are scheduled to start in Geneva on January 25.
"The political process will begin, we hope, as soon as possible, at the end of January," he said.
"We don't know the actual date yet, but we are going to go forward and support the recommendations, particularly the ones made by Mr Staffan de Mistura, UN special envoy for Syria.
"The UN Security Council is obliged to make sure that this meeting of all the Syrian actors and players takes place soon and we hope very much that it will be in this month."
Kerry did not make any comments on Wednesday, but his spokesman John Kirby said in a statement that the two men had "discussed plans for the UN-led negotiations between the Syrian parties on January 25 and the importance of maintaining progress toward a diplomatic solution to the crisis in Syria".
READ MORE: US 'takes control' of Rmeilan airfield in Syria
Before leaving Washington on Tuesday, Kirby had acknowledged that "there is still quite a bit of work that needs to be done to get the meeting to occur" between Syrian President Bashar al-Assad's regime and representatives of the opposition.
In Wednesday's meeting, Kerry called for Russia to use its influence with Assad "to ensure immediate, unimpeded and sustained humanitarian access to all Syrians in need," Kirby said, particularly in besieged communities such as Madaya, where deaths from starvation have been reported.
Lavrov said the pair "confirmed the need to resolve the humanitarian problem in Syria".
Source: Al Jazeera and agencies