The comments came from Syria's former deputy premier Qadri Jamil, who was sacked by President Bashar al-Assad in 2013 and now heads the so-called Moscow Group, an opposition faction close to the Kremlin which has met repeatedly with UN envoy Staffan de Mistura at negotiations in Geneva.
When the Syria peace process was relaunched in January, the UN recognised the Saudi and Western-backed High Negotiations Committee (HNC) as the official opposition delegation.
Jamil however said that approach was not working.
The Moscow Group has "asked that all opposition groups be merged into one delegation... The current situation with several delegations is not normal. It should not continue," Jamil said.
He also said the UN should organise face-to-face meetings between the opposition and regime, after previous rounds have seen the sides meet separately with mediators.
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The HNC suspended its participation at the Geneva talks last week to protest restrictions on humanitarian access on the ground and escalating violence, accusing the regime of repeatedly violating a ceasefire in place since February 27.
Unlike the HNC, Jamil's group has not insisted that Assad step down before a transitional government is formed.
But the ex-premier said that divisions between various camps should not stop Syrian opposition groups from meeting the regime as a single delegation.
At the current round of talks, which began on April 13, Jamil's faction has been meeting de Mistura alongside the so-called Cairo Group, which is also tolerated by the regime.
The UN envoy has also met with a Syria-based opposition faction, considered very close to the government.
De Mistura is due to give a progress report to the UN Security Council on Wednesday, when the talks are scheduled to go into recess.
Syria's war began as a pro-democracy revolt in 2011, but later morphed into a civil war that has left more than 270,000 people dead after the regime unleashed a brutal crackdown against dissent.