Rifts on energy and trade overshadow EU-Russia summit

* EU, Russia leaders meet near Chinese border

* Kremlin warns over trade, gas

* Both sides seek to strike upbeat tone

By Conor Sweeney

KHABAROVSK, Russia, May 22 (Reuters) - The leaders of the European Union and Russia will struggle to overcome deep rifts on energy supplies and trade at a summit on Friday near the Chinese border.

Russia and the EU say they want to improve ties after rows over gas supplies via Ukraine and Moscow's war last year with Georgia. But diplomats say discord is simmering just below the surface.

On the eve of the summit, the Kremlin cautioned there could be sparring over energy and trade while a Russian government source warned of another gas crisis with Ukraine.

Russia's Foreign Ministry said it was tired of "absurd political delays" to work on a new bilateral framework agreement with the EU.