The UN has failed to break a deadlock at Syrian peace negotiations in Geneva, with talks interrupted after the government railed against a US decision to resume aid to the opposition.
There was also no movement on Tuesday towards getting aid to besieged residents in Syria's central city of Homs, where UN trucks were waiting for access to deliver desperately needed food and medical supplies.
After a difficult morning meeting on the fourth day of talks, UN mediator Lakhdar Brahimi said he decided to cancel afternoon discussions and reconvene the parties for "what I hope will be a better session" on Wednesday morning.
"Nobody is walking out, nobody is running away," Brahimi told reporters. "We have not achieved any breakthrough, but we are still at it, and this is good enough as far as I'm concerned."
A member of the opposition negotiating team, Rima Fleihan, told the AFP news agency that Brahimi adjourned the meeting "because the regime is not cooperating on any subject, not on humanitarian issues and not on a transitional governing body".
She said the opposition had presented a preliminary transition plan laying out its "vision" for Syria, but the government refused to engage in talks.
Also on Tuesday, delegates from President Bashar al-Assad's government presented a statement they wanted adopted, which condemned Washington for "arming terrorist groups in Syria".
"This decision can only be understood as a direct attempt to obstruct any political solution in Syria through dialogue," the statement said.
A State Department spokesman, Edgar Vasquez, dismissed accusations of Washington supporting terrorism as "ludicrous".
"The Assad regime is a magnet for terrorists. The regime's brutality is the source of the violent extremism in Syria today," he said in a statement. "We support the moderate political and military opposition who are fighting for the freedom and dignity of all the Syrian people."
Syrian peace talks had initially resumed on Tuesday with the UN hoping to break a deadlock over a possible transitional authority, but the opposition said the government refused to discuss it.
Brahimi had earlier said Tuesday's talks would focus on the Geneva communique, the text agreed by world powers in 2012 that calls for the creation of a transitional governing body in the country.
Al Jazeera's diplomatic editor James Bays, reporting from Geneva, said that unlike on previous days, news crews had not been allowed to film delegates arriving.
He said Brahimi had also warned both sides against making "inflammatory statements" to the press.
The two sides have been brought together in the biggest diplomatic push yet to end a civil war that has left more than 130,000 people dead and forced millions from their homes.
Expectations are low for a breakthrough, especially after the two sides failed to agree on even the basic principles of political talks on Monday.