KYIV, Oct 11 (Reuters) - Ukrainian President Volodymyr Zelenskiy on Tuesday asked the leaders of the Group of Seven (G7) nations for more air defence capabilities to stop Russia, and to back his initiative for an international observer mission on the Belarusian border.Joining the G7 leaders' virtual meeting a day after missiles rained down on Ukrainian cities including the capital Kyiv, Zelenskiy called for tough new sanctions on Moscow and again ruled out talks with Russian President Vladimir Putin."When Ukraine receives a sufficient quantity of modern and effective air defence systems, the key element of Russia’s terror, rocket strikes, will cease to work," Zelenskiy said, thanking German Chancellor Olaf Scholz for speeding up delivery of the IRIS-T air defence system and U.S. President Joe Biden for deliveries of air defence systems.Ukraine's Western allies have pumped aid and heavy weapons to Kyiv since Russia's invasion in February.Ukraine has no plans to attack Belarus, Zelenskiy said, but wants to make sure there is no threat from its northern neighbour."