US President Donald Trump has promised new weapons for Ukraine and set a 50-day deadline for Russia to reach a peace deal or face tough sanctions.

The deal to arm Ukraine was announced in the Oval Office in a joint press conference with NATO Secretary General Mark Rutte.

Trump, who said he was losing patience with Russian President Vladimir Putin, said the US would supply weapons that would 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.

Trump coupled the arms announcement with a vow to impose “100 per cent” tariffs and sanctions on Russia if it failed to make a ceasefire agreement within 50 days.

Trump said he was deeply frustrated with Putin. He said Putin was pleasant to speak to on the phone, but then went on to unleash withering bombing raids on Ukraine.

“I don’t want to say he’s an assassin, but he’s a tough guy,” Trump said.

Trump also revealed how his wife Melania had helped change his thinking on Putin.

“I go home, I tell the first lady, ‘You know, I spoke to Vladimir today, we had a wonderful conversation’. She said, ‘Oh, really? Another city was just hit’,” Trump said.

He added that the Kremlin leader had “fooled a lot of people”.

“He fooled Clinton, Bush, Obama, Biden. He didn’t fool me, but what I do say is that at some point, ultimately, talk doesn’t talk.

“It’s got to be action. It’s got to be results.”

Rutte and Trump announce an arms deal for Ukraine. Photo: AAP

Trump’s decision to send arms to Ukraine represents a turning point for the Republican President.

Trump spent the early months of his term trying to coax Putin into a ceasefire agreement only to be turned down every time.

He said “top of the line” equipment, including Patriot missile systems and batteries, would be arriving “very soon — within days”.

Ukraine President Volodymyr Zelensky has made regular appeals to the US and its NATO military allies for weapons to help defend itself in the grinding war.

Tariffs threat

US Congressional leaders are working on a Russia sanctions package.

A White House official said Trump wanted to impose “100 per cent tariffs on Russia” and secondary sanctions on nations that bought oil from Russia if a deal was not struck in 50 days.

“We’re going to be doing secondary tariffs,” Trump said.

“If we don’t have a deal in 50 days, it’s very simple, and they’ll be at 100 per cent.”

“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.

A White House official said Trump was referring to 100 per cent tariffs on Russian goods, as well as secondary sanctions on other countries that buy its exports.

Still, Trump’s announcement of a 50-day grace period was greeted with relief by investors in Russia, where the rouble recovered from earlier losses and stock markets rose.

“Trump performed below market expectations. He gave 50 days during which the Russian leadership can come up with something and extend the negotiation track. Moreover, Trump likes to postpone and extend such deadlines,” said analyst Artyom Nikolayev from Invest Era, a financial information firm.

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 wanted to be part of re-arming 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 will pay for the weapons satisfies his demand that the US not continue bankrolling the war and puts the financial burden on US allies in Europe.

Zelensky on Monday said he would replace his long-serving prime minister Denys Shmyhal with Shmyhal’s first deputy, Yulia Svyrydenko, in “a transformation of the executive branch”.

The nomination, which requires parliamentary approval, comes as diplomatic efforts to end the war, now in its fourth year, have stalled and as Ukraine seeks to revive its cash-strapped economy and build up a domestic arms industry.

“We … discussed concrete measures to boost Ukraine’s economic potential, expand support programs for Ukrainians, and scale up our domestic weapons production,” Zelensky wrote on X.

“In pursuit of this goal, we are initiating a transformation of the executive branch in Ukraine,” he said, adding that he had proposed that Svyrydenko lead the government and “significantly renew its work”.

Svyrydenko, 39, is an economist by training and has been first deputy prime minister since 2021.

-with AAP