Steffan De Mistura said UN would choose delegation if opposition could not agree ahead of talks later this month.
Syria’s main opposition body said on Wednesday it would be unacceptable for the United Nations to choose its delegation to peace talks scheduled to take place in Geneva later this month.
The next round of UN-based peace talks on Syria have been scheduled for 20 February, diplomats said on Tuesday.
The UN envoy for Syria, Staffan de Mistura, has said the UN would choose the opposition’s representatives if they cannot agree on their delegation, “in order to make sure that it can be as inclusive as possible.”
However the Saudi-backed High Negotiations Committee, the main opposition umbrella group, rejected the suggestion on Twitter. “De Mistura’s talk of his intentions to form the opposition delegation himself is unacceptable,” said its spokesman Salim al-Muslit.
“Would de Mistura be able to intervene in forming the regime’s delegation?” asked the HNC, which includes political and armed groups and represented the opposition in peace talks last year.
HNC chief coordinator Riad Hijab said on Twitter: “Selecting the Syrian opposition delegation is not de Mistura’s business.”
The Syrian government and rebel groups opposed to President Bashar al-Assad began a nationwide ceasefire in late December, brokered by Moscow and Ankara.
The UN-sponsored talks had been planned to begin in Geneva on 8 February but Russia’s Foreign Minister Sergei Lavrov said last week they had been postponed. Invitations to the talks are due to go out on that day.
De Mistura on Tuesday said the talks had been postponed to 20 February in part to give the opposition more time to present a united delegation and to take advantage of last week’s indirect talks between the Syrian government and opposition in the Kazakh capital of Astana.
Those talks ended without any major breakthrough, though a nationwide Syria truce brokered by Russia and Turkey has largely held since it began on 30 December.
More than 310,000 people have been killed in Syria since the conflict erupted with anti-government protests in March 2011