Geneva, Switzerland (CNN) -- Delegations for the Syrian government and the Syrian opposition will meet in the same room on Saturday -- a day later than originally planned.
U.N. special envoy Lakhdar Brahimi made the announcement on Friday after he met separately with each side to apparently prevent an immediate breakdown in efforts to end Syria's civil war.
However, the fragility of the process was made clear when an opposition spokesman told reporters that Saturday's meeting still would have Brahimi as a go-between, instead of direct exchanges between the two sides.
"Everybody will be in the same room, but everyone will address Mr. Brahimi," said Louay Safi of the main opposition group, the Syrian National Coalition.
The delegations originally were scheduled to sit down in the same room on Friday in Geneva, but Brahimi said he needed more time to set up the session.
While Brahimi's announcement represented progress to overcome such an early hurdle, it also demonstrated the difficulty of even getting the two sides into one room to start negotiations on ending violence that has claimed more than 100,000 lives since 2011.
Earlier, Syrian state TV reported that Syrian Foreign Minister Walid al-Moallem told Brahimi that if a serious meeting was not held Saturday, "the Syrian official delegation will leave Geneva because of the lack of seriousness and readiness" of the opposition.
Meanwhile, the opposition delegation warned that it would not take part in any direct talks unless it saw movement on the issue of a transitional government -- that is, that the government shifts on its position that President Bashar al-Assad will remain in power.
Speaking after Brahimi announced the Saturday meeting, Safi said the two sides agreed that the talks would address all the points of a 2012 agreement for ending the war, including a transitional government, releasing political prisoners and access for humanitarian assistance.
The first priority for the opposition was discussing the formation of a transitional governing body with full power, including control of the Syrian military, Safi said, adding the opening phase of the negotiations would last a week.
U.S.: rough road ahead
U.S. State Department spokesperson Jen Psaki welcomed the news of the Saturday talks, saying "such a meeting is a positive step forward in what we expect will be a long and complicated process."
"We reiterate the same point we have made all day: You should not perceive every obstacle or challenge that arises throughout the process as a deal-breaker or a collapse," Psaki said.
Earlier, Secretary of State John Kerry said in a speech at the World Economic Forum in Davos that "we know it's going to be very, very hard." At the same time, Kerry noted that diplomacy had already shown some hope by leading the al-Assad regime to turn over its known chemical weapons stockpile.
The fighting has made Syria "the world's greatest single individual magnet for jihad and terror," Kerry said, making clear that the United States supports the opposition position that al-Assad must go.
"Because of the havoc he has wreaked on his people, Assad will never have the legitimacy to govern Syria," Kerry said.
The war has become increasingly sectarian, drawing in Syria's regional neighbors and forcing out more than 2 million refugees, many of them children.
However, the warring Syrian sides remain far apart.
In a preliminary international session held Wednesday in nearby Montreux, Syria struck a defiant tone, laying a record of atrocities -- rape, arson, even the destruction of Syrian culture itself -- at the feet of rebels and chiding outsiders for trying to interfere.
No one had the right to withdraw al-Assad's legitimacy, Moallem said.
Meanwhile, the leader of the Syrian National Coalition made clear that it sees no role for al-Assad in a transitional government.
Ban: Nobody said this would be easy
U.N. Secretary General Ban Ki-moon urged both sides to persist with the talks.
"We had extremely hard negotiations this week on Syria; nobody said this would be an easy process," Ban told CNN's Richard Quest in Davos.
He also said that Iran was "one of the important regional powers who can contribute to this process" but that he believed he made the right choice in rescinding an invitation to Tehran to join the talks in Geneva.
The Syrian National Coalition had said it would pull out if Iran was invited, because Tehran has not signed on to the framework agreed in 2012 that envisages a political transition.
"I regretfully made the decision I did. It was of greater importance to have the two sides together," Ban said, referring to the Syrian government and opposition.
While the stakes for the talks are high, observers see little likelihood that the conference will find a way to end the violence in Syria. But analysts say there is hope that progress can be made on improving the situation for the most vulnerable victims of the civil war.
The Syrian National Coalition does not represent all the opposition groups in Syria, making it uncertain that any agreement it may reach in Geneva would be respected on the ground.
A military representative may join the Syrian opposition team, opposition members said.
CNN's Nic Robertson and Elise Labott reported from Geneva for the report written by Laura Smith-Spark in London and Tom Cohen in Washington. CNN's Gayle Edmonds and Saad Abedine contributed to this report.