The week of negotiations in Geneva, Switzerland, were largely fruitless, and U.N. special envoy Lakhdar Brahimi apologized for the failure to make any significant progress.
"I am very, very sorry, and I apologize to the Syrian people that ... we haven't helped them very much," he said.
The major obstacle, he said, was the desire of the Syrian government to talk about dealing with terrorism, while the opposition wanted to discuss setting up a transitional government.
Brahimi said the government rejected a plan to start the next round of talks with one day reserved for each of the issues.
The rejection "raises the suspicion of the opposition that in fact the government doesn't want to discuss the [transitional government] at all," he said.
Brahimi said negotiators for both sides should consider "do they want the [peace] process to take place or not?"
The only agreement produced by the talks allowed civilians in Homs to leave the besieged city and for aid to enter.
The envoy said his next step would be to consult with U.N. Secretary-General Ban Ki-moon.
The Syrian government has called demands by opposition rebels "unrealistic," saying the rebels' desire to create a transitional government is a non-starter because President Bashar Assad will not step down, the BBC said.
The opposition says Syria has not shown "any responsiveness."
U.S. President Barack Obama said late Friday a "diplomatic solution" for the Syrian crisis must be found, the Voice of America reported. He did not think an immediate solution was possible, but said steps would be taken to "apply more pressure" to Assad.
Also Friday, the U.N. Security Council discussed a draft resolution that expressed "grave alarm" about civilians trapped by Syrian forces. Russia has threatened to veto the resolution, saying it was weighted against the Syrian government.
The conflict, now in its third year, had killed more than 136,000 people and caused millions more to flee their homes, the United Nations says.