It would be "an enormous mistake to refuse to cooperate with the Syrian government", Russian President Vladimir Putin has said.

Putin made remarks while addressing the general debate of the UN General Assembly, which opened here on Monday, Xinhua news agency reported.

"We think that it is an enormous mistake to refuse to cooperate with the Syrian government and its armed forces who are valiantly fighting terrorism face to face," said Putin.

"We should finally acknowledge that no one but President Assad's forces and the Kurdish militia are truly fighting the IS and other terrorist organisations in Syria."

Putin said Moscow's approach to Syria has drawn criticism but insisted this was only because Russia was more honest and frank about its ambitions than its critics.

"It is not about Russia's ambitions but about the recognition of the fact that we can no longer tolerate the current state of affairs in the world," he said.

Putin also took aim at a proposal put forward by France to limit the use of the veto in the UN Security Council.

"The veto right has always been exercised -- by the US, the UK, France, China, and Russia alike -- it is absolutely natural for so diverse and representative organisation," he said, referring to the five permanent members who have veto power on the UN Security Council.

"When the UN was established its founders did not think there would always be unanimity," he said. "The mission of the organisation is to seek and reach compromises and its strength comes from taking different views and opinions into consideration."

Over 140 heads of government are expected to speak at this year's general debate of the 193-member General Assembly in commemoration of the 70th anniversary of the founding of the UN.