US Secretary of State John Kerry Sunday blamed 'obstruction' by the regime of President Bashar al-Assad for the breakdown in talks in Geneva between the sides in Syria's civil conflict.

"None of us are surprised that the talks have been hard, and that we are at a difficult moment, but we should all agree that the Assad regime's obstruction has made progress even tougher," Kerry said.

In a statement released here, Kerry urged the regime's supporters to press for the creation of a transitional government, warning they would bear the responsibility "if the regime continues with its intransigence in the talks and its brutal tactics on the ground."

The peace talks broke off Saturday with no result at the end of a second round of negotiations seeking an end to the brutal three-year-old conflict.

No date was set for a third round of talks and it was unclear whether any would be held, but Kerry said the United States remained committed to the Geneva process and all diplomatic efforts to find a political solution.

"There's no recess in the suffering of the Syrian people, and the parties and the international community must use the recess in the Geneva talks to determine how best to use this time and its resumption to find a political solution to this horrific civil war."

More than 140,000 people have died and millions have been driven from their homes since the conflict began.

A monitoring group said this week more than 5,000 people had been killed since the talks began on 22 January.