President Trump said on Sunday he's strongly opposed to Russian President Vladimir Putin's actions in Ukraine while peace negotiations continue.

"I'm not happy with what Putin is doing. He's killing a lot of people and I don't know what the hell happened to Putin. I've known him a long time," he said before returning to the White House for Memorial Day.

"I've always gotten along with him but he's sending rockets into cities and killing people and I don't like it at all. Okay? We're in the middle of talking and he's shooting rockets into Kyiv and other cities. I don't like it all," he added.

Trump said he is "very surprised" by Putin's latest actions.

"Something happened to this guy and I don't like it," he said.

Trump told reporters he's "absolutely" considering additional sanctions against Russia, given their ongoing attacks on Ukraine.

"I don't know what's wrong with him. What the hell happened to him, right? He's killing a lot of people, I'm not happy with that," he said.