The Russian army is moving at a “glacial pace” and struggling to gain ground more than three years after its invasion — but it still could take years and major losses for Ukraine to reclaim all the territory Moscow has taken since 1991, according to military analysts.

The Ukraine war saw a major shift on Tuesday after President Trump claimed for the first time that Kyiv can push back Russia’s forces and liberate 20% of the country currently occupied by the Kremlin.

Such a feat, however, would come at a high cost that would force Ukraine’s military to ramp up enlistment, weapons production and develop a fully fledged air force and navy, Seth Jones, of the Center for Strategic and International Studies (CSIS) think tank, told The Post.

“It will be hard, but not impossible to take back the territory,” he said. “The big challenge so far in the Ukrainian war is that the conflict has largely given the advantage to whoever is on defense.”

Moscow has been sluggish to gain ground since attacking Ukraine in February 2022, with the Kremlin’s troops now moving at a “glacial pace,” Jones said.

In the past 20 months, Russia’s forces have only managed to take 1% more of Ukraine, with Moscow barely able to make any dents against Kyiv’s fortress belt cities in Donetsk, according to the CSIS and the Institute for the Study of War (ISW), a fellow Washington-based think tank monitoring the war.

The slow advancement is compounded by the massive losses Moscow has faced, with the Russian casualties estimated at 1 million, according to the last CSIS analysis in June.

The estimates include 250,000 dead soldiers, which is about five times greater than all the losses faced in the previous Soviet and Russian wars since World War II combined.

In the last 20 months, Russia was also estimated to have lost more than 4,100 armored vehicles and 1,800 tanks. the CSIS reported.

If Ukraine were to switch to the offense, it would likely face similar losses, Jones warned.

“The fighting has provided the side on defense with the chance to dig trenches and place minefields. It all makes it difficult for the offense to push through without suffering massive casualties like what we’ve seen from Russia,” Jones said.

One of the biggest challenges for Kyiv would be the manpower needed to fight offensively, with Ukraine’s military already dealing with 60,000 to 100,000 deaths.

And unlike Russia, Ukraine does not have an advanced air force or navy to conduct joint operations with its army, which only makes an offensive battle even more difficult, Jones added.

Although it would face serious challenges, Peter Doran, of the Foundation for Defense of Democracies think tank, agreed that Ukraine is fully capable of winning back its territories if it receives the full backing of the US and NATO.

“To break the stalemate, Ukraine needs sustained military support, and Russia’s economy needs a blow from the US and Europe,” Doran said, referencing recent pushes for secondary sanctions against Moscow.

“With all this support, Ukraine’s prospects of winning back its territory is high,” he added.

Should Ukraine be successful in pushing Moscow’s forces back, the Kremlin could retaliate by waving around its nuclear arsenal to avoid humiliation.

“They thought about doing that back in the fall of 2022 when they were being pushed back in Crimea,” Jones pointed out. “That would risk a big escalation.”

The reality that Ukraine can take back its land — regardless of the high costs involved — should be enough to worry Moscow.

“Trump put his finger on a war that Russia is just not winning,” Jones said. “There is truth to what he said about Russia’s army being a ‘paper tiger.’

“It’s true that Russia’s army is not an effective fighting force,” he added.

After speaking with Ukrainian President Volodymyr Zelensky this week, Trump boasted that Kyiv was poised to “win all of Ukraine back” with backing from the US and Europe.  

“[Vladimir] Putin and Russia are in BIG Economic trouble, and this is the time for Ukraine to act,” Trump added. “Let [Ukraine] get their land back.”

Kremlin spokesperson Dmitry Peskov pushed back on Trump’s claims Wednesday, insisting Russia’s economy was fine and describing Moscow’s army as a “bear” rather than a paper tiger.

Peskov said that in light of Trump’s remarks, Russia has “no alternative” but to continue its invasion of Ukraine, suggesting a cease-fire deal is still off the table.