RIYADH: A meeting between Syrian opposition groups in Riyadh has ended in stalemate, a member said Tuesday, with the fate of President Bashar al-Assad still an obstacle in forming a unified front for peace talks.

The Saudi-backed opposition High Negotiations Committee (HNC) began discussions on Monday with delegations from two other moderate camps, the so-called Cairo and Moscow groupings, in a bid to reach consensus on a joint negotiating strategy.

After hosting seven rounds of largely unsuccessful talks, U.N. Syria envoy Staffan de Mistura had sought to unify the opposition for what he hopes will be a substantive round of negotiations in October.

"The representatives of the Moscow grouping refused to recognise any text that referred to the Syrian people's demand for the departure of Bashar al-Assad," said Ahmed Ramadan of the National Coalition, a leading component of the HNC.

"There was an important level of understanding between HNC and the Cairo grouping, but the stalemate with Moscow group delegates hampered efforts to bring representatives... into a single negotiating delegation."

There was no immediate comment from the so-called Moscow group.

Assad's fate has long been a key sticking point, with the HNC insisting on his ouster but the other two camps adopting a softer stance.

De Mistura said last week that he hopes for "real" peace talks between the government and a still-to-be-formed unified Syrian opposition in October.

Rebels have suffered heavy territorial losses since peace talks to end the war began, including the regime's recapture of second city Aleppo, a former opposition stronghold.

With the rebel fighting position weakened, experts say the regime faces no pressure to make concessions at the negotiating table, and especially not over the question of Assad's future.