President Donald Trump on Monday announced a toughened stance against Russia for its war in Ukraine, promising a fresh wave of missiles and other weaponry for Ukraine and giving Moscow 50 days to reach a ceasefire or face sanctions.

In the Oval Office at an announcement with NATO Secretary General Mark Rutte, Trump told reporters he had become deeply frustrated with Russian President Vladimir Putin.

The decision by Trump to send arms to Ukraine represented a turning point for the Republican president, who has spent the early months of his term trying to coax Putin into a ceasefire agreement, only to be turned down every time.

READ: Trump gives Russia 50 days to resolve Ukraine war

Under the deal, Trump said the U.S. will supply weapons that will be paid for by NATO countries. Rutte said massive numbers of weapons would be sent, including missiles, as part of a first wave of equipment.

Ukraine President Volodymyr Zelenskiy has made regular appeals to the U.S. and its NATO allies for weapons to help defend itself in the grinding war.

Trump coupled his arms announcement with a vow to impose tariffs and sanctions on Russia if Moscow will not make a ceasefire agreement within 50 days.

Congressional leaders have been working on a Russia sanctions package.

A White House official said Trump's intent is to impose "100% tariffs on Russia" and secondary sanctions on other countries that buy oil from Russia if a deal isn't struck in 50 days.

"If I was Vladimir Putin today, and you're speaking about what you are planning to do in 50 days... I would reconsider whether I should not take negotiations about Ukraine more seriously," Rutte said.

Trump has been reluctant to punish Russia, but he came away from a recent phone call with Putin disappointed that the Russian leader appeared prepared to continue the war.

Rutte said Germany, Finland, Denmark, Sweden, Norway, the Netherlands and Canada all want to be a part of rearming Ukraine.

"They all want to be part of this. And this is only the first wave. There will be more. So what we will do is work through the NATO systems to make sure that we know what Ukrainians need to make packages," he said.

Trump's promise that NATO would pay for the weapons satisfies his demand that the U.S. not continue bankrolling the war and puts the financial burden on U.S. allies in Europe.

(Production: Arlene Eiras)