"We deeply regret that this round did not make any progress," Syria's deputy foreign minister, Faisal Muqdad told reporters as both sides traded blame over the deadlock in the Geneva talks, the second round of which began Monday.
Speaking separately just minutes earlier, opposition spokesman Louay Safi complained about the other side's failure to budge.
"The negotiations have reached an impasse," Safi said.
"If this situation does not change... It means that the negotiations are not moving towards a political solution. We are now awaiting serious progress."
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The opposition insists peace talks must centre on Syria's political transition from one-party rule under President Bashar al-Assad.
But government negotiators have refused to discuss a 24-point plan by the opposition to craft a transition body to halt violence and pave the way for elections.
The regime side, which insists Assad's future cannot be up for debate, wants the talks to focus on "terrorism" -- the label applied to the three-year revolt, which it says has been fuelled by foreign jihadists and Gulf money.
"Those who carry arms against their people and government are terrorists," he said.
The opposition rejects such arguments hands down.
It underlines that the Free Syrian Army is itself battling Al-Qaeda-linked fighters, and has spotlighted regime inaction against the jihadists and even alleged complicity.
It also accuses the regime of terrorism due to its tactic of raining "barrel bombs" onto opposition-held communities, and of deploying fighters from the Iranian Revolutionary Guards and the Iranian-backed Lebanese Shiite militia Hezbollah, classed as a terrorist group in the West.