Peace talks between the Syrian regime and opposition fighters got off to a shaky start after the rebels refused to negotiate face to face in the first session and the representative for Assad’s government described remarks by his opposite number as insolent and provocative.

The negotiations sponsored by Russia, Iran and Turkey in the Kazakh capital, Astana, are the latest attempt to end the five-year civil war, and are seen as a test of Moscow’s influence in the Middle East.

A leaked draft communique for the talks broadly supports the existing UN talks process, and proposes the establishment of a trilateral commission to oversee monitoring of the ceasefire. It also calls for joint action to defeat Islamic State and other terrorist groups in Syria.

For the first time, the opposition delegation has been drawn from the armed rebel groups rather than their political representatives. The talks are designed to build on the fragile ceasefire that came into force in late December after the fall of the rebel stronghold of east Aleppo.

Mohammed Alloush, the leader of the opposition delegation, said the existence of Iranian-sponsored militias alongside regular Syrian government troops made peace more difficult to achieve, and called for them to leave the country. He also called for the release of prisoners from government jails, saying 13,000 women were being held arbitrarily.

Alloush insisted the political process would begin with the departure of Bashar al-Assad, Iran, and their militias – a set of demands that put the opposition at loggerheads with the regime.

His remarks were denounced as insolent by Bashar al-Jaafari, the leader of the Assad delegation and the Syrian ambassador to the UN.

In his opening statement, Alloush said the opposition was focused on bolstering the nationwide truce.

“We came here to reinforce the ceasefire as the first phase of this process,” he said. “We will not proceed to the next phases until this actually happens on the ground.”

A rebel spokesman said the first negotiation session was not held face to face because of the regime’s continued bombardment and attacks on an area near Damascus.