President Vladimir Putin acknowledged Sunday that Russia is facing a "certain shortage" of fuel following a wave of repeated Ukrainian strikes targeting oil refineries and domestic supply lines.

"As for strikes against critical infrastructure in general, and energy infrastructure in particular, of course, these attacks on our infrastructure facilities create problems," Putin said in a Kremlin-published interview. "That's obvious."

"Right now we're observing a certain shortage, but it's not critical," he added.

The government's primary focus, Putin said, was to improve Russian air defense system capabilities and to ensure that fuel supplies reach consumers, especially in annexed Crimea, where local authorities declared a state of emergency last week.

A few hours earlier, in a speech at the congress of the ruling United Russia party, Putin had vowed to restore security and overcome mounting challenges as Ukraine intensifies its retaliatory strikes against Russia.