U.N. Syria envoy Staffan de Mistura said on Tuesday that U.S. President-elect Donald Trump was right to seek to work with Russia to beat Islamic State group in Syria, but urged him to help push for political reforms to stop the militant group gaining recruits.

Speaking on the BBC's Hardtalk programme, de Mistura said it was crucial to fight IS group, also known as Daesh, but that a long-term victory required "a completely new approach" to a political solution.

"In other words, some type of political devolution in Syria. Otherwise many other people, unhappy in Syria, may join Daesh while they are fighting Daesh," he said.

De Mistura presided over a fitful Syrian peace process in the first half of this year, but it finally stalled because cooperation collapsed between its two chief backers, U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov.

While Russia has maintained strong support for Syrian President Bashar al-Assad, whom it regards as a bulwark against "terrorists", the United States has said Assad must leave power under any political transition.

Although the U.N. Security Council has mandated a political transition process, Assad's government has refused to consider any formula that might involve a dilution of his power.

Many of Trump's opponents fear that his stated intention to work more closely with Russian President Vladimir Putin means the United States would withdraw support for Syrian opposition groups and agree to Assad staying in power.

De Mistura said he had not yet been contacted by anyone in Trump's team, but that was to be expected because of the focus on U.S. internal politics. But he looked forward to hearing from, and briefing, Trump's foreign policy pick.

Mistura said he expected the United States, regardless of policy, to remain a fundamental player in trying to resolve the crisis in Syria.