A discontented Donald Trump has given Vladimir Putin a two-week ultimatum for a ceasefire, cautioning of a different course of action if Putin is “stringing us along”.

This warning from the US president comes amidst Russia’s most lethal attacks on Ukraine to date, with Kyiv expressing concern that Moscow is gathering forces for a significant new assault.

In the Oval Office on Wednesday, Trump expressed his disapproval, saying: “I’m very upset about the events of the past couple of nights where lives were lost during what should be a negotiation.”

He added: “When I see rockets being shot into cities, that’s no good. We’re not going to allow it.”

When asked if Putin really wants to end the war, Trump replied: “I can’t tell you that, but I’ll let you know in about two weeks.

“Within two weeks. We’re gonna find out whether or not he’s tapping us along or not.

“And if he is, we’ll respond a little bit differently.”

The US president’s comments came just minutes after Russian Foreign Minister Sergei Lavrov proposed a second round of talks with Ukraine in Istanbul.

He said the proposed talks on June 2 would be a continuation of negotiations.

Kyiv has said it’s “not opposed” to meetings.

The White House has recently ramped up efforts to secure a ceasefire deal between Russia and Ukraine.

Trump and Putin had a two-hour phone call on May 19, after which Putin said he was ready to work with Ukraine on a “memorandum on a possible future peace agreement”.

But the US has been accused of appeasing Moscow – notably, when the White House shifted its focus from a 30-day unconditional ceasefire (agreed on only by Ukraine) and recently opted for a summit with Putin.

The US has however rejected these claims, pointing out that all sanctions against Russia remain firmly in force.

The Kremlin has not yet sent a memorandum, claiming it’s currently drafting a version and that there cannot be a fixed deadline for ceasefire details to be agreed.

Meanwhile, over the past few days, Trump has lashed out at Putin on social media.

He said on Tuesday that Putin has gone “absolutely crazy” and is “playing with fire” after Russia intensified its attacks on Ukraine.

Trump added that “lots of bad things” would have happened to Russia if it were not for his involvement.

The US president broke his silence on Sunday after Russia fired 367 drones and missiles at Ukrainian cities in the largest aerial attack of the war now in its fourth year.

Russian strikes in Kyiv killed at least 13 people, including three children, and injured dozens more.

Putin has been building up a 50,000-strong force alongside the border of Kharkiv, for an offensive in the eastern region of Sumy, according to Ukrainian President Volodymyr Zelensky.

On Tuesday, it was revealed that Putin’s forces had seized another four villages in Ukraine’s Sumy region.

Sumy governor Oleh Hryhorov wrote in a post: “The enemy is continuing attempts to advance with the aim of setting up a so-called buffer zone”.

Hryhorov said the villages of Novenke, Basivka, Veselivka and Zhuravka had been overrun, with their residents evacuated.

In response, Ukraine launched hundreds of drone strikes on the Russian capital overnight into Wednesday morning.

The strikes hit Moscow and 11 other regions, disrupting flights to and from the capital, Russia’s Defense Ministry reported.

Zelensky has accused Moscow of delaying the peace process and claimed Ukrainian intelligence shows Putin has no intention of ending the war.

To end Europe’s deadliest war since WWII, the Russian president wants a “written” pledge from Western leaders to stop Nato’s expansion to countries eastward, top Russian officials revealed to Reuters.

The eastward expansion refers to Ukraine, Georgia, Moldova and other former Soviet republics.