Top diplomats from the United States and Russia were to meet in Geneva on Tuesday to prepare for planned Syrian peace talks to be held in the Swiss city, dpa reported.
No date has been fixed for the peace talks, which have been hit by delays and by conditions from the Syrian government and opposition.
On Tuesday morning, senior US and Russian officials were to meet Lakhdar Brahimi, the UN and Arab League's envoy on Syria.
A meeting with counterparts from the other permanent UN Security Council members - China, Britain and France - was scheduled for the afternoon.
The Syrian National Coalition, Syria's main opposition grouping, said on Sunday it would not take part in peace talks without a timetable for Syrian President Bashar al-Assad to leave office.
Al-Assad has said that foreign support for the rebels must stop, so a political solution can be reached.
The United Nations estimates that more than 100,000 people have been killed since the Syrian conflict began in 2011.