The U.N. special envoy for Syria, Staffan de Mistura, said Friday that he had met with a "substantial" delegation from the Syrian government.
Friday's meeting was a preparatory one, de Mistura told reporters.
Substantive talks will have to wait until members of an umbrella opposition group called the High Negotiations Committee arrive in Geneva, which de Mistura said wouldn't be before Sunday or Monday.
The committee told CNN on Friday it will take part in the peace talks. They said they decided to participate in the talks to test the seriousness of the Syrian government, through negotiations with the United Nations team.
The HNC earlier had threatened to boycott unless the government of Syrian President Bashar al-Assad regime lifts sieges and stops bombarding civilians.
The head of the committee told CNN's Christiane Amanpour that they were awaiting a response from the United Nations about those points.
"We told Mr. de Mistura that these principles are above the negotiation, that they are final (and) cannot be discussed or compromised," said Riyad Hijab, head of the High Negotiations Committee.
De Mistura had urged the opposition to come regardless of whether the government complies with opposition demands to show good faith actions such as releasing prisoners, ending siege's of rebel-held territories.
U.S. Secretary of State John Kerry issued a statement praising the HNC decision to attend, calling it an "important decision."
"The United States further expects that both sides in these negotiations will participate in good faith and achieve early, measurable progress in the days ahead," Kerry said.
Kurds invited, but as observers
Syrian Foreign Minister Walid Moallem was not expected to be in Geneva, the source close to the talks said. But on Friday, a CNN team at the U.N. building in Geneva did see de Mistura welcome the Syrian delegation led by that country's Permanent Representative to the U.N. Bashar Ja'afari.
SANA, Syria's state news agency,
reported that the delegation's meeting with de Mistura began at 5 p.m. (11 a.m. ET) Friday.
The talks were originally set to begin in Geneva on Monday, but were delayed because of ongoing discussions about who should represent the opposition, de Mistura told reporters this week
There are Kurds invited, but as observers -- not to negotiate. The opposition committee and the government are the only ones empowered to negotiate.
'We need to hear your voice'
The talks mark the first time in two years that the warring sides in Syria meet in an effort to find a political way out.
Past efforts to negotiate an end to the conflict have been hindered by strong opposition to the Assad regime, which is perceived as brutal, and by the fractured nature of the opposition, which includes ISIS as well as more moderate groups supported by the United States.
The plan calls for proximity talks, which means the parties will be in separate rooms, with de Mistura shuttling between them.
De Mistura's video message Thursday said the talks would start "in the next few days." Syrians on all sides, he said, should make sure their representatives know how important it is to strike a deal.
"We need to hear your voice to everyone who is coming to this conference ... saying this conference must be an opportunity not to be missed," de Mistura said.