BEIRUT (Reuters) - The Syrian opposition will announce on Saturday its delegates for the next round of U.N.-based peace talks in Geneva planned for later this month, the main opposition umbrella group said.

The choice of opposition delegates has been subject to disagreement and the U.N. envoy for Syria, Staffan de Mistura, has said it would choose the opposition delegates if they could not agree, "to make sure that it can be as inclusive as possible."

The Saudi-backed High Negotiations Committee (HNC), Syria's main opposition body which includes political and armed groups, has criticised Mistura's comment as "unacceptable".

HNC spokesman Salim al-Muslit told Arabic news channel Arabiya al-Hadath on Saturday that following meetings in Riyadh, Syrian opposition officials would present the 20-member delegation they have chosen to attend the talks.

The HNC represented the opposition in peace talks last year, but was not invited to the Kazakh capital Astana, where indirect talks between government and rebel delegates were held last month.

Moscow and Ankara brokered a shaky nationwide ceasefire in December between the Syrian government and rebel groups opposed to President Bashar al-Assad.

The next round of United Nations-sponsored talks on the Syrian conflict, now in its sixth year, have been scheduled for Feb. 20.

Muslit said the opposition delegation would bring together various groups, which, as well as the HNC would include rebel factions that took part in Astana negotiations. It will also include Kurdish, Turkmen and Christian representatives, he said, but did not elaborate.

"It is a military political delegation and it represents everyone," Muslit said. "Each component will nominate the person it finds suitable."

Twenty legal advisors will accompany the negotiators to Geneva, he added.

An opposition official on Saturday confirmed to Reuters a report by al-Arabiya news channel that Nasr al-Hariri, of the Syrian National Coalition group, will head the delegation.

Meanwhile, the Kazakh Foreign Ministry said delegations from the Syrian government and rebels, along with de Mistura, have been invited to attend meetings in Astana on February 15-16.

Despite an overall reduction of violence, fighting and air strikes have tarnished the fragile ceasefire. More than 600 people have died in clashes and bombardment since the truce began, the Syrian Observatory for Human Rights war monitor said.

(Reporting by Ellen Francis and Tom Perry in Beirut, Ahmed Tolba in Cairo, and Reem Shamseddine in Khobar; Editing by Clelia Oziel)