The Syrian government's lead negotiator has denounced what he called his rebel counterpart's "provocative" comments at the start of peace talks in Astana.
Bashar Jaafari said Mohammed Alloush had acted in a way "removed from diplomacy" at the indirect negotiations convened by Russia, Iran and Turkey.
Mr Alloush described the Syrian government as a "terrorist entity".
He also said a political solution to the civil war was the rebels' preferred choice, but "not the only one".
More than 300,000 people have been killed and 11 million others displaced since the uprising against President Bashar al-Assad began in March 2011.
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The talks opened on Monday morning at a hotel in Astana with the rebel delegation sat on one side of a large round table, and government officials on the other side.