BEIJING, Nov 20 (Reuters) - China's president told his Iranian counterpart to seize the opportunity to improve relations with world powers, as diplomats hope to clinch a preliminary deal to curb Iran's nuclear programme in charged talks resuming in Geneva on Wednesday.

The United States, Russia, China, France, Britain and Germany came close to winning concessions from Iran on the scope of its nuclear work in return for some sanctions relief at negotiations in the Swiss city on Nov. 7-9.

Policymakers have said that an interim accord on steps to start defusing a decade of hostility between the West and Iran could be within reach during talks this week.

President Xi Jinping praised Iranian President Hassan Rouhani for his government's "proactive conduct" on nuclear talks and its efforts to improve relations with the international community, the official Xinhua news agency said late on Tuesday.

"China hopes Iran seizes the opportunity, maintains the dialogue momentum, and seeks the greatest common factor to strive for the best results," Xinhua cited Xi as saying in a phone call with Rouhani.

China will continue to exert a proactive influence in six-party talks to create conditions for a long-term resolution, Xi said.

The last round of talks stumbled over Iran's insistence that its "right" to enrich uranium be recognised, and disagreement over its work on a heavy-water reactor near Arak, which could yield plutonium for atomic bombs once it becomes operational.

Iranian Foreign Minister Mohammad Javad Zarif has since indicated a way around the first sticking point, saying Tehran has the right to refine uranium but is not insisting others recognise that right.

Western governments suspect Iran has enriched uranium with the covert aim of developing the means to fuel nuclear weapons, a charge Tehran denies. Refined uranium can also fuel nuclear power plants - Iran's stated goal.

A shift towards meaningful diplomacy between Iran and the world powers began after the June election of Rouhani on a platform to relieve the country's international isolation and get sanctions strangling its oil-dependent economy lifted.

(Reporting by Michael Martina; Editing by Michael Perry)