US President Donald Trump on Sunday expressed anger with Russian President Vladimir Putin and threatened secondary tariffs on Russian oil should the two not reach a deal to stop fighting in Ukraine.

The reported comments come amid the Trump administration's push to end to the war between Russia and Ukraine.

Trump 'angry' with Putin over call for new administration in Ukraine

NBC journalist Kristen Welker said Trump had called her in an exclusive interview and expressed his frustration at the Russian leader.

"If Russia and I are unable to make a deal on stopping the bloodshed in Ukraine, and if I think it was Russia's fault — which it might not be — but if I think it was Russia's fault, I am going to put secondary tariffs on all oil coming out of Russia," said Trump.

The threat of 25% tariffs on Russian oil could happen at "any moment," Welker quoted Trump as saying, and added that the president planned on speaking with Putin this week.

"I was very angry, pissed off when Putin started getting into Zelenskyy credibility and started talking about new leadership in Ukraine," Trump told Welker, referring to Ukrainian President Volodymyr Zelenskyy.

During his presidential campaign, Trump promised to bring an end to the war soon after his second term in office began in January.

Trump and Putin have had two publicly announced telephone calls, the last known communication taking place on March 19.

Trump warns Zelenskyy against backing out of mineral deal

Separately, Trump later warned Zelenskyy not to back out of the minerals deal with the US.

"I see he's trying to back out of the rare earth deal," Trump said, speaking to reporters aboard the Air Force One.

If Zelenskyy does that, "he's got some problems, big, big, problems," the US president added.

Trump also said Ukraine is "never going to be part of NATO," and that Zelenskyy understands that.

Putin pushes to remove Zelenskyy

On Friday, Putin floated the idea of Ukraine being brought under a UN-sponsored "transitional administration" that would that would oversee elections in the country before a peace agreement is negotiated.

The White House said it was up to Ukrainians and their constitution to determine the country's governance.

The Ukrainian constitution prohibits elections during wartime, and allies believe Putin would use a fresh election to try and install a pro-Russian head of government.

Russia, Ukraine accuse each other of violating partial energy ceasefire

Russia and Ukraine had agreed on a moratorium on targeting energy infrastructure earlier this month, but both Kyiv and Moscow have accused the other of violating the agreement.

Russia and Ukraine had also agreed separately to avoid military strikes on vessels in the Black Sea.

Ukraine accuses Russia of war crime for strike on hospital

Meanwhile, Ukraine on Sunday accused Russia of committing a "war crime" during a weekend attack on the city of Kharkiv.

Ukrainian officials said six strikes hit the northeastern border city overnight, wounding personnel receiving treatment at a military hospital.

At least two people were killed in a residential building, the officials said.

Dmytro Chubenko, spokesperson for the Kharkiv regional prosecutor's office, confirmed two deaths and said another 30 people were wounded, including children.

Edited by: Roshni Majumdar, Srinivas Mazumdaru