Ukraine is battling to hold a chunk of Russian territory it has occupied for months, with experts saying the results could impact a reported demilitarisation zone plan that Donald Trump is reportedly considering to end the war.
Ukrainian President Volodymyr Zelenskyy said his country is fighting some 50,000 Russian and North Korean troops in the Kursk region, following an audacious ground incursion there in August.
The operation took Moscow by surprise, with Ukrainian officials saying the move was crucial in forcing Kremlin soldiers away from other parts of the frontline under heavy attack.
Now Ukraine has said it is pushing troops back to pressure points on the eastern front amid growing pressure from Russia.
"(Russian forces) are trying to dislodge our troops and advance deep into the territory we control," Mr Zelenskyy said of the Kursk fighting on Telegram this week.
[MAP]At the time of the counteroffensive into Kursk, which secured Ukraine a chunk of Russian land, Mr Zelenskyy said it could be used as a future bargaining chip.
With Trump now returning to the White House and promising peace, some experts agree.
Trump considering permanent freezing of frontline
Three insiders with knowledge of the proposal told the Wall Street Journal (WSJ) that a 1,200 kilometre zone would be introduced, effectively holding the front-line in place.
That would be coupled with security deals from Western countries, including the US, to supply Ukraine with weapons to bolster defences into the future.
But exactly how the zone would operate remained unclear.
"We can do training and other support but the barrel of the gun is going to be European," one member of Trump's team told the WSJ.
"We are not sending American men and women to uphold peace in Ukraine. And we are not paying for it. Get the Poles, Germans, British and French to do it."
Other reports suggest Ukraine could be forced into giving up land occupied by Russia — some 20 per cent of its country — for peace.
That would include Crimea, which Russia annexed in 2014, along with large swathes of the Donbas, Zaporizhzhia and Kherson regions.
Mr Zelenskyy has repeatedly ruled out ceding any land.
Russian President Vladimir Putin has ruled out stopping the war until his annexations are recognised internationally.
There are also questions over whether Ukraine will be pushed to promise not to join NATO under a proposed peace deal.
Trump has long been frustrated with the amount of US aid being sent to Ukraine, which has topped $US175 billion.
He has also criticised European countries for not providing enough funding the North Atlantic Treaty Organization (NATO), which the US is the top funder of.
US Secretary of State Antony Blinken will travel to Brussels to discuss support for Ukraine in meetings with NATO and European Union counterparts this week, the US State Department said.
Kursk region a 'bargaining chip'
A Russia expert at foreign policy think-tank Chatham House, John Lough, told the ABC it was "no coincidence" that the Russian and North Korean troop build-up had taken place in Kursk in the lead-up to the US election.
"They want to demonstrate to Trump and the new administration that this war is going in one direction, that the Ukrainians are steadily losing, and that if there is no longer going to be large-scale US support, then Ukraine has to put up the white flag," Mr Lough said.
He said Russia wanted to reclaim the area entirely, but the feasibility of achieving the goal wasn't clear.
Trump has repeatedly said he could end the war in "24 hours" without detailing how.
Mr Lough said Kursk could become critical to either side depending on what Trump has in mind.
"It could be a bargaining chip for Ukraine if they manage to hold their position there and if Trump indicates he's expecting … a temporary ceasefire to see if they can work something out, then the Russians will be stuck with a problem," he said.
The area would also likely be used in any potential land-swap deal, which Mr Lough believed was looking increasingly likely at some point.
Trump's challenge to land a peace deal
Director of the Ukrainian Centre for Defence Strategies think tank, Alexander Khara, said Ukraine was unlikely to agree to any such demilitarisation zone deal proposed by Trump.
"It's not going to fly," Mr Khara told the ABC from Ukraine's capital, Kyiv.
"He will not be able to impose an … armistice on Ukraine because it is not compatible with the survival of the Ukrainian state or its future."
He also said ceding any territory to Russia wasn't feasible.
He said if Russia held Crimea, which it illegally annexed in 2014, it would continue to threaten both Ukraine and Europe because of its strategic location to the Black Sea.
"The Soviet Union's Black Sea fleet was designed to project its power into the Mediterranean, to pose a threat to NATO and the region … with nuclear-capable cruise missiles," he said.
Mr Lough said Trump's campaign promise to end the war in a day might come back to haunt him.
"I suggest a campaign slogan is going to collide with reality because he's going to discover that this issue is much more complex than he initially thought," he said.
Russia denied that the president-elect warned Mr Putin not to escalate the war in a a phone-call this week.
That apparent call came around the time Russia and Ukraine launched massive aerial assaults.
Mr Lough said Trump can't give Russia everything it wants and would need to balance calls to guarantee Ukraine's ongoing security.
"The last thing he wants to do is look weak in front of the Chinese, the Iranians and others because he has set the stage for himself as the tough president who is going to keep the pressure on these people and he wants them to be afraid of him," he said.
