New U.S. sanctions hit top Russian firms; Kiev says Russia shoots down its jet

A pro-Russian separatist from the Vostok (East) battalion poses for a picture atop a T-64 tank in Donetsk, eastern Ukraine, July 16, 2014. REUTERS/Maxim Zmeyev

WASHINGTON/MOSCOW (Reuters) - President Barack Obama imposed sanctions on some of Russia's biggest firms for the first time, striking at the heart of Vladimir Putin's powerbase by targeting companies closest to him over Moscow's failure to curb violence in Ukraine.

In the latest escalation of the conflict on the Ukrainian-Russian frontier, Kiev said a Russian jet had shot down one of its warplanes, its strongest accusation yet of direct Russian military involvement in the war. A Ukrainian military spokesman said the pilot of the SU-25 fighter ejected to safety.