New Delhi, June 29 -- Ukraine kept up its heavy drone assault on Russia, setting fire to a major oil refinery in the south, as President Vladimir Putin acknowledged for the first time on Sunday that the country was facing a "certain deficit" of fuel and vowed to strengthen protection of oil facilities and boost fuel output.

Ukraine has markedly stepped up its long-range attacks on Russian military industries and energy facilities in recent months, aiming to cut Moscow's revenue for its invasion - now in its fifth year - and make Russians feel the consequences.

"Our 'long-range sanctions' reached two oil refineries in Russia," Ukrainian President Volodymyr Zelenskyy wrote on the Telegram messaging app on Sunday. "Each (strike) means a re...