By VASILISA STEPANENKO and LORNE COOK

KYIV, Ukraine (AP) — Ukrainians welcomed U.S. President Donald Trump’s pledge of more U.S.-made weapons in their three-year fight against Russia’s invasion, though it is unclear what exactly they will get and how quickly.

The time frame for the further arms deliveries, which European countries have agreed to pay for, is crucial. Russia is making a summer push to break through along the 1,000-kilometer (620-mile) front line, and its drones and missiles are hammering Ukrainian cities more than at any time in the war.

Ukrainian President Volodymyr Zelenskyy thanked Trump for his “willingness to support Ukraine.” In Kyiv, resident Nina Tokar, 70, said Tuesday that with more U.S. weapons going to Ukraine “maybe this will all end faster.”

However, following Trump’s threat late last week to impose major sanctions on Russia for failing to reach a deal to end the fighting, the American president said Monday that Moscow would get 50 days to come to a settlement or face “very severe” economic sanctions.

While some believe strict tariffs on Moscow could be a game changer, the decision to postpone them until September struck some European observers as being too long. Ukrainian officials made no direct comment about the 50-day window, but for Russia, the delay of new sanctions came as a reprieve.

Senior Russian lawmaker Konstantin Kosachev commented: “Oh, how much can change both on the battlefield and with the mood of those leading the U.S. and NATO in 50 days.”

Russian President Vladimir Putin hasn’t budged when presented with previous U.S. deadlines and threats. In an interview with the BBC broadcast Tuesday, Trump said of Putin: “I’m disappointed in him, but I’m not done with him.”

Russian Foreign Minister Sergey Lavrov said Moscow “would like to understand what is behind this statement about 50 days,” noting that the Kremlin has offered to continue direct peace talks with Ukraine.

“Earlier, there were also the deadlines of 24 hours and of 100 days,” Lavrov said during an official trip to China. “We’ve seen it all and really would like to understand the motivation of the U.S. president.”

An assessment published Tuesday by Chatham House noted that “the exact details of what has been agreed remain hazy.”

“Putin will continue to judge Trump by his actions, not by his words — and so far, there is little enough action to be seen,” the London-based think tank said.

Military experts are trying to figure out whether Russian forces could use the window left by Trump to achieve significant territorial gains.

Russian troops are slowly ramming through the Ukrainian defenses in Ukraine’s eastern Donetsk region, the main focus of the Russian offensive. They are also trying to carve out a buffer zone along the border with the northeastern Ukrainian regions of Sumy and Kharkiv.

Russia currently holds about 20% of Ukraine. Ukraine’s depleted army has recently been losing more territory, but there is no sign of a looming collapse on the front line, analysts say.

Zelenskyy said he spoke to Trump after the Republican leader’s Oval Office announcement Monday on weapons sales, expressing gratitude for the decision to send more Patriot air defense missiles that are vital to defend Ukrainian cities.

“We discussed … the necessary measures and decisions to provide greater protection for people from Russian attacks and strengthen our positions,” Zelenskyy said on Telegram. “We agreed to talk more often and coordinate our steps in the future.”

Trump and Zelenskyy have had a notoriously fraught relationship, and Washington’s consent to providing more weaponry has eased Kyiv’s worries.

Even so, some Ukrainians felt the U.S. decision won’t alter the course of the war. “If we take the situation as a whole, it hardly looks like this will fundamentally change anything,” Kyiv resident Oles Oliinyk, 33, told The Associated Press.

Tokar, the Kyiv resident, was also skeptical. “I have very little faith in (Trump). He says one thing today, and tomorrow he may say something else.”

Dutch Foreign Minister Caspar Veldkamp expressed misgivings about the 50-day delay on sanctions.

“I do believe that the 50 days that Mr Trump has announced is rather long. It’s up to September 2. I think that’s rather long,” he said in Brussels on Tuesday.

Much remains to be worked out about how and when the weapons, especially the Patriot systems, will be provided, Denmark’s Foreign Minister Lars Løkke Rasmussen said.

But, in an indication that Europe is relieved that the U.S. hasn’t walked away from the conflict, he added: “The most important thing is that we now have an American readiness to deliver these most needed weapons.”

Some European countries, such as Hungary and Slovakia, still rely heavily on Russia for energy supplies and could be hit hard by Trump’s threatened secondary sanctions on countries that buy its oil and gas — an effort to isolate Moscow in the global economy.

Lithuania’s Foreign Minister Kęstutis Budrys said Trump’s 50-day delay was a “signal for Europe to prepare ourselves, because we still have some member states that are exposed to imports of oil and oil products from Russia.”

German Defense Minister Boris Pistorius said it remains to be seen whether Trump’s announcement will be a turnaround but “what is decisive is that the tone has changed.” The president’s threat to impose sanctions after 50 days is “significant progress,” Pistorius told ARD television.

Cook reported from Brussels.

Follow AP’s coverage of the war in Ukraine at https://apnews.com/hub/russia-ukraine