Peace talks have entered their fifth day in Geneva on Wednesday with no progress on a transfer of power or providing needed humanitarian relief.
UN envoy for Syria Lakhdar Brahimi says Syrian delegations will continue negotiations until Friday.
Despite their frustration, each side vowed it would not be the first to walk away from the talks.
Brahimi said Geneva II has not achieved a breakthrough, but nobody has walked out yet.
The Syria peace talks finished early Tuesday amid opposition demands that the government address the question of a transition of power. Opposition spokesmen said they wanted the Syrian government to have time to come up with a proposal on the issue.
Asked why the afternoon session of the Tuesday talks was cancelled, Brahimi responded: "It's my own decision taken without any pressure from any of the two parties."
He added that both delegations would continue negotiations until Friday. Brahimi also announced that an aid convoy to the besieged Syrian city of Homs was on standby awaiting authorization from the Syrian government.
Brahimi also said that a convoy bearing humanitarian aid was still waiting to enter besieged parts of the city of Homs. The government has offered to allow women and children to leave opposition-held areas, and to grant safe passage to men as well if they receive a list of their names.
