OSCE member states were Thursday battling to thrash out a compromise on an action plan that would bolster the clout of the trans-Atlantic security group after its first summit in over a decade.

World leaders at the summit, hosted by Kazakhstan in its glitzy new capital Astana, have acknowledged the Organization for Security and Cooperation in Europe (OSCE)'s reactions to prevent conflicts in Europe and the ex-USSR have slowed in recent years.

But the 56 member state group operates by consensus, meaning any single country could torpedo a final communique and framework for action that diplomats hope will define its future role.

"I hope that in the remaining moments we can agree a declaration and overcome the differences," Kazazkh President Nursultan Nazarbayev told the final session of the summit.

"I am counting on your flexibility. History has given us a unique chance and it would be unforgivable to lose it."

"We still have a job to be finished. We need to show that we can have a consensus," added Lithuanian President Dalia Grybauskaite, whose country will hold the OSCE chairmanship next year.

Leaders including US Secretary of State Hillary Clinton and Russian President Dmitry Medvedev had the day before urged a revamp of the OSCE to better cope with modern security threats.

The last such summit dates back to a 1999 meeting in Istanbul.

However diplomats told AFP the deal still risks being snagged on references to specific controversial issues including the Armenia-Azerbaijan dispute on Nagorny Karabakh and the rebel Moldovan region of Transdniestr.

But particular controversy comes from references to Georgia, which fought a war with Rusisa in 2008 over two breakaway regions which Moscow now recognises as independent.

Russian Foreign Minister Sergei Lavrov said that Moscow would not accept any document containing a reference to an ongoing "conflict" in Georgia or an insistence on the country's territorial integrity.

Most of the top leaders left after the first day of the summit, leaving their diplomats to rush to agree a deal for Nazarbayev to announce at a news conference scheduled for 0600 GMT.