U.S. President Donald Trump said Sunday he was confident of bringing resolution to the conflict between Russia and Ukraine.

Trump described Russia's war as a "waste of great humanity" and said he was "not happy with anything having to do with that war."

He said he expected to speak with Russian President Vladimir Putin in the next couple of days and acknowledged that the conflict had proved harder to resolve than he anticipated.

"Look, we're going to get it done. The Russia-Ukraine situation, we've got to get it done," he said.

Russia hit Ukraine's capital with drone and missiles Sunday in the largest aerial attack since the war began, killing four people across the country and damaging a key government building.

Russia attacked with 810 drones and decoys, Ukraine's air force said, adding it shot down 747 drones and four missiles.