Representatives from the Syrian government and the Western-backed opposition faced each other briefly Saturday in their first-ever joint meeting aimed at resolving nearly three years of civil war.
Officials say the first session in Geneva lasted only about 30 minutes, with both sides sitting in silence while only U.N. mediator Lakdar Brahimi spoke.
Another session is expected Saturday, with the two sides speaking only to Brahimi on humanitarian issues.
U.S. State Department spokesman Edgar Vasquez said the opposition demonstrated "a seriousness of purpose" in Geneva and went to the meeting "with the intention to engage constructively."
Another U.S. official, speaking on background, said as innocent civilians die in Syria, the regime continues to play games.
Syria's government had threatened to walk out of peace talks with the opposition if the two sides did not begin what it called "serious sessions" by Saturday. The opposition has said it will not negotiate directly with the Syrian government unless it agrees to discuss the departure of President Bashar al-Assad.
Damascus has refused, accusing the rebels of supporting terrorism.
However, Brahimi has said the larger issues would be set aside and talks would deal with modest issues and build on them to achieve bigger issues.
On Friday, U.S. Secretary of State John Kerry stepped up criticism of Mr. Assad, calling him a "one-man super-magnet for terrorism" that "will never earn back legitimacy" to bring his country back together.
Speaking at the World Economic Forum Friday in Davos, Switzerland, Kerry said that if the goal is to have peace in Syria, Mr. Assad needed to step down because the opposition would never stop fighting while he is in power. He said the embattled president has brought "havoc" on Syrians, unleashing bombs and "gassing his own people in the dead of night."
Kerry added the world has seen how forceful diplomacy can achieve goals in Syria, as a man who once refused to admit he had chemical weapons has now removed them from his arsenal.
The official goal of the so-called Geneva 2 talks is to form a Syrian transition government, though analysts say the chances of achieving this goal are slim.
The Syrian conflict began in March 2011 as peaceful protests before spiraling into a civil war that the U.N. says has killed well over 100,000 people and forced nearly 9 million from their homes.