Russia's foreign minister has accused the United States of using peace talks to seek "regime change" in Syria.
Speaking in Moscow on Friday, Foreign Minister Sergey Lavrov said the issue of a transitional government, a key focus for opposition negotiators, must not dominate the talks in Switzerland.
"We have an impression that those backing the opposition in this process... had in mind only one thing, regime change," Lavrov said, noting the talks were "going in circles."
His comments came a day after senior US and Russian officials met in the Swiss city with UN mediator Lakhdar Brahimi, in an effort to save faltering talks between the Syrian government and opposition.
Brahimi was meeting separately with Syria's warring sides on Friday.
Lavrov's deputy, Gennady Gatilov, has also waded into the fray, saying Syria's government would discuss the creation of a transitional governing body if the opposition officially declared its commitment to join the fight against "terrorism".
Gatilov, whose comments were reported by Russian news agencies on Friday, said the Syrian government delegation had no plans to pull out of the talks.
Al Jazeera's James Bays, reporting from Geneva, said Brahimi had been looking to the US and Russia to break the deadlock, but "it seems they have now blocked it further."
Brahimi plans to take Syrian peace talks into a third round, an opposition official said on Friday.
"Brahimi just told us the talks will continue and there will be a third round, but he did not set a date," opposition negotiator Ahmad Jakal told Reuters news agency.
The faltering talks come amid a backdrop of increased violence, with the United Nations voicing concern on Friday over a Syrian government military build-up in the rebel-held town of Yabroud.
Hundreds of Syrians have fled Yabroud, fearing an imminent attack, a UN spokesperson told Reuters.
"We have received reports from within Syria that there have been numerous aerial attacks and shelling along with a military build-up around the town, suggesting a major assault by land may be imminent," UN human-rights spokesman Rupert Colville said.
Meanwhile, a senior UN official in Syria said the evacuation of civilians from besieged areas of the city of Homs had been put on hold until the fate of the detained men from rebel-held areas became clear, according to a report by the Associated Press news agency.
Matthew Hollingworth said on Friday that dozens of men and boys aged 15 to 55 who were evacuated from Homs during a days-long truce between Syrian forces and rebels were still being questioned by Syrian authorities.
The governor of Homs, Talal Barazi, told Al Jazeera that media would be allowed into the facility where the men of "fighting age" were being questioned, and that the process was being monitored by the UN.