President Donald Trump on Saturday said he won’t waste time meeting Russian President Vladimir Putin again unless a deal on the war in Ukraine is likely.

It was earlier announced that Trump would meet Putin in Budapest to advance the talks on a peace deal in Ukraine, but the meeting never materialized.

European allies - buffeted by Trump's swings between accommodation and anger toward Putin - hope he keeps upping the pressure on Moscow, and are also mulling major actions of their own.

A key figure in Ukraine's 3-month-old campaign to outfox its larger enemy by targeting oil facilities deep inside Russia with drones said Moscow was improving its ability to intercept them, but that his unit was forging technology to keep one step ahead.

Russia targeted Ukraine's capital with drones, killing three people in their homes, local authorities said early on Sunday.

Both sides are targeting energy assets to try to break the deadlock on the battlefield.