(Bloomberg) -- A Russian offensive in eastern Ukraine appears imminent even as Kyiv holds out for more weapons deliveries for its own push in the south in the spring, according to assessments from US and European officials.

Still, the officials cautioned that neither side is likely to gain much ground soon in a war that remains very bogged down. Russia is less likely to drive down from the north through Belarus in a coming offensive, the people said, asking not to be identified discussing sensitive information.

The latest assessments indicate that while the array of arms already sent from the US, Europe and other allies — from ammunition to artillery to tanks and longer-range missile defenses — is helping Ukraine hold Russian forces back, it is not enough for a substantial recouping of territory before Moscow’s offensive. More weapons are coming but not for some months. And that could mean the conflict lasts at least through this year.

The assessments echo warnings from Ukrainian leaders in recent days and promise some difficult weeks ahead for its forces, who now face as many as 300,000 Russian troops along the front lines — considerably more than the initial invasion almost a year ago.

The concerns follow what many military analysts had described as a winter transition in the war, when the battlefield stabilized after two stunning Ukrainian counter-offensives in the fall. President Vladimir Putin’s mobilization of troops — while poorly trained and equipped — has consolidated Russian defensive lines through the winter and they may soon be thrown into the attack.

“We are on the eve of a very active phase,” Andriy Yusov, a representative for the Ukrainian Defense Ministry’s intelligence service, said on Wednesday, calling the current situation “very difficult.” 

“There will be very active battles in February and March,” he added.

The prospect of a war that now drags into 2024 could play to Russia’s advantage if it can continue to cling onto territory, potentially forcing President Volodymyr Zelenskiy’s hand in any future negotiations. 

Zelenskiy has repeatedly said he will not cede an inch of Ukrainian territory in talks and that Kyiv will insist that Crimea, annexed by Russia in 2014, is returned. But while allied support for Ukraine is strong for now, a war that goes for years could test that resolve.

Given the time needed for delivery, training and building supply lines, advanced battle tanks from Europe and the US may not appear on the battlefield until later in the spring. When they do come they will give Ukraine a much-needed boost. Its military has already had greater success in recent months in shooting down missiles fired by Russia at its cities and energy infrastructure, helped by air systems sent in by its allies.

The US is advising Ukrainian forces to play for time to allow those tanks and other weaponry to arrive, according to a senior official. In order to gather resources for a spring offensive in the south, Ukraine may also have to withdraw its troops soon from the eastern town of Bakhmut, US and European officials said, handing Russia a symbolic victory.

The situation “is becoming even more severe” for Ukraine’s forces in the east, Zelenskiy said on Wednesday in his regular nightly address. “There is a certain increase in the occupiers’ offensive actions at the front.” 

Russia’s also learning from mistakes to a certain degree. It has withdrawn equipment from areas within reach of long-range artillery, built more defensive infrastructure like obstacles and trenches in northern Crimea and deployed more mines. It is also operating shorter logistics lines, according to a senior NATO official. And Moscow’s efforts to recruit more soldiers will force Kyiv to expend more ammunition at a time when supplies are running low.

Still, Ukraine has rebounded from tactical defeats and defied predictions of succumbing to a stalemate several times during the war and could well do so again. 

A retreat from Bakhmut would not have a major strategic impact on the war, the officials said. Ukraine’s troops would likely establish defensive lines very close to where the current front line is, a senior US official said. 

Russia’s army continues to incur heavy casualties on the battlefield with a strategy of throwing waves of troops into the fight to try to gain ground. While it might be calling up more soldiers it will struggle to train recruits with many mid-ranking officers already killed in battle, according to NATO officials.

From Bakhmut, Russia is expected to push toward Slovyansk and Kramatorsk. Its forces are unlikely to succeed in taking the entirety of the eastern Donetsk region anytime soon, given the vast size of territory to cover. 

Both sides will likely seek to draw on an element of surprise, meaning the timings and locations of assaults could always change depending on how the war develops.

A focus by Ukraine on the south through spring and summer could open up opportunities around Crimea with Russia’s military supplies cut off, several officials said. Ahead of that, Russia may attempt to push Ukrainian forces as far north as possible, away from Crimea, which is clearly a prize for Putin and something he wants to protect above all.

A senior US official said it was unlikely Ukraine could retake Crimea anytime soon, adding the government in Kyiv is focused on more immediate goals that are challenging enough.

Still, should Ukraine succeed in regaining territory in the south around the area of Melitopol and split Russian lines between Crimea and the east of the country by the end of the summer, Kyiv would set the stage for a difficult few months for Putin and his forces.

--With assistance from Marc Champion , Daryna Krasnolutska and Tom Hall.

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