Donald Trump said he has sealed an agreement with Nato allies that will lead to large-scale arms deliveries to Ukraine, including Patriot missiles, and warned Russia that it will face severe sanctions if Moscow does not make peace within 50 days.

After a meeting with the Nato secretary general, Mark Rutte, Trump said they had agreed “a very big deal”, in which “billions of dollars’ worth of military equipment is going to be purchased from the United States, going to Nato … And that’s going to be quickly distributed to the battlefield.”

Speaking in the White House alongside a clearly delighted Rutte, the US president said the arms deliveries would be comprehensive and would include the Patriot missile batteries that Ukraine desperately needs for its air defences against a daily Russian aerial onslaught.

“It’s everything: it’s Patriots. It’s all of them. It’s a full complement, with the batteries,” Trump said.

He did not go into any more detail, but made clear the weapons would be entirely paid for by Washington’s European allies, and that initial missile deliveries would come “within days” from European stocks, on the understanding they would be replenished with US supplies.

At a White House lunch with religious leaders later in the day, Trump said the deal was “fully approved, fully done”.

“We’ll send them a lot of weapons of all kinds and they’re going to deliver those weapons immediately … and they’re going to pay,” he said.

At his meeting with Trump, Rutte said there was a significant number of Nato allies – including Germany, Finland, Denmark, Sweden, Norway, the Netherlands and Canada – ready to rearm Ukraine as part of the deal.

“They all want to be part of this. And this is only the first wave. There will be more,” he said.

The German chancellor, Friedrich Merz, said last week that Berlin was ready to acquire additional Patriot systems.

Trump claimed there was one country, which he did not name, but which had “17 Patriots getting ready to be shipped”. Monday’s deal would include that stockpile, or “a big portion of the 17”, he said.

Such an arms delivery would represent a significant reinforcement of Ukraine’s air defences. Kyiv is currently thought to have only six Patriot batteries, at a time when it is coming under frequent and intense Russian drone and missile bombardments.

At the same time, Trump expressed increased frustration with Vladimir Putin, whom he accused of giving the impression of pursuing peace while intensifying attacks on Ukrainian cities. He gave the Russian president a new deadline of 50 days to end the fighting or face 100% tariffs on Russian goods, and more importantly, sweeping “secondary tariffs”, suggesting trade sanctions would be imposed on countries who continue to pay for Russian oil and other commodities.

“The secondary tariffs are very, very powerful,” the president said.

The announcement marked a dramatic change for the administration, both in substance and tone.

The Trump White House had not only made clear it would continue its predecessor’s policy of continuing to supply Ukraine out of US stocks, but the president and his top officials have been derisive about Kyiv’s chances of prevailing.

On Monday, Trump delivered his most admiring language on Ukraine and its European backers to date, with Rutte on one side and the US vice-president, JD Vance, the administration’s biggest sceptic on US involvement in Europe, on the other.

“They fought with tremendous courage, and they continue to fight with tremendous courage,” Trump said of the Ukrainians.

“Europe has a lot of spirit for this war,” he said, suggesting he had been taken by surprise by the level of commitment shown by European allies at the Nato summit in The Hague last month. “The level of esprit de corps spirit that they have is amazing,” he said. “They really think it’s very, very important.

“Having a strong Europe is a very good thing. It’s a very good thing. So I’m okay with it,” he said.

Trump described his deepening disillusion with Putin, and suggested his wife, Melania, may have played a role in pointing out the Russian leader’s duplicity in talks over a peace deal.

“My conversations with him are always very pleasant. I say, isn’t that a very lovely conversation? And then the missiles go off that night,” Trump said. “I go home, I tell the first lady: I spoke with Vladimir today. We had a wonderful conversation. She said: Really? Another city was just hit.”

Ukrainian regional officials reported at least six civilians killed and 30 injured by Russian bombing in the past 24 hours. The country’s air force said Moscow had attacked with 136 drones and four S-300 or S-400 missiles.

“Look, I don’t want to say he’s an assassin, but he’s a tough guy. It’s been proven over the years. He’s fooled a lot of people,” Trump said, listing his predecessors in the White House.

“He didn’t fool me. But what I do say is that at a certain point, ultimately talk doesn’t talk. It’s got to be action,” he said.

Russian officials and pro-war bloggers on Monday largely shrugged off Trump’s announcement, declaring it to be less significant than anticipated.

Konstantin Kosachev, a senior Russian lawmaker, wrote on Telegram that it amounted to “hot air”.

It was broadly welcomed in Kyiv, where there has been longstanding and deep anxiety about Trump’s intentions. Andrii Kovalenko, a member of Ukraine’s national security and defence council, posted a one-word response: “Cool.”

There was still scepticism however, over whether even the promise of new weaponry for Ukraine combined with the threat of trade sanctions would be enough to halt Russia’s offensive.

Illia Ponomarenko, a Ukrainian journalist and blogger wrote: “How many Ukrainian lives could have been saved if, from the very beginning, Trump had listened to wise and honest people about helping Ukraine, instead of the artful lies of that cannibal Putin on the phone?”.