People cross the Irpin River next to a destroyed bridge, amid Russia's invasion of Ukraine, outside of Kyiv. Reuters

He added that Moscow and Kyiv could also settle on a peace deal very soon.

The exact timing of Russia’s exit from Ukraine would depend on how much resources the Kremlin was willing to commit to the campaign.

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 “I think that no later than in May, early May, we should have a peace agreement, maybe much earlier, we will see, I am talking about the latest possible dates,” Arestovich said.

He added: “We are at a fork in the road now: there will either be a peace deal struck very quickly, within a week or two, with troop withdrawal and everything, or there will be an attempt to scrape together some, say, Syrians for a round two and, when we grind them too, an agreement by mid-April or late April.”

Russia invaded Ukraine on 24 February, after weeks of denying such plans.

The adviser added that a “completely crazy” scenario could also involve Russia sending fresh conscripts after a month of training.

However, even after peace deal is struck, Russia could engage in small tactical clashes for a year,  Arestovich said, adding that Ukraine will push for complete exit of Russian soldiers from its soil.

Russia invaded Ukraine on 24 February, after weeks of denying its plan so and called its move a “special military operation”.

Meanwhile, a senior US defence official has said that Russia’s military advances outside of a number of cities in Ukraine have “stalled”. There has been no “appreciable” change on advances on the capital city of Kyiv or the country’s second-largest city of Kharkiv, but the southern port city of Mariupol is “isolated”.

A convoy of more than 160 cars departed from Mariupol on Monday, according to local officials, in what appeared to be the first successful attempt to arrange a “humanitarian corridor” to evacuate civilians from the besieged Ukrainian city.

People have been trapped in Mariupol for more than two weeks and are reportedly running out of supplies after being surrounded by Russian forces.

Ukraine’s president has sent a letter of condolence to the family of an American journalist killed in the war zone, and said his entire country is mourning with them.

Brent Renaud, 50, a renowned American filmmaker, was killed when Russian troops opened fire over the weekend close to Kyiv.

The Independent