Ukraine’s defence minister has said Russia is preparing a major new offensive, and warned that it could begin as soon as 24 February.
Oleksii Reznikov said Moscow had amassed thousands of troops and could “try something” to mark the anniversary of the initial invasion last year.
The attack would also mark Russia’s Defender of the Fatherland Day on 23 February, which celebrates the army.
Mr Reznikov said Moscow had mobilised some 500,000 troops for the offensive.
In September, Russian President Vladimir Putin announced a general mobilisation of some 300,000 conscripted troops, which he said was necessary to ensure the country’s “territorial integrity”.
But Mr Reznikov suggested that the true figure recruited and deployed to Ukraine could be far higher.
“Officially they announced 300,000 but when we see the troops at the borders, according to our assessments it is much more,” he told the French BFM network. The BBC cannot independently verify this figure.
Despite some heavy fighting in the eastern Donbas region, the war has entered something of a stalemate in recent months since Ukraine retook the southern city of Kherson.
With the exception of the Russian seizure of the town of Soledar, neither side has made major territorial advances.
But Mr Reznikov said Ukraine’s commanders would seek to “stabilise the front and prepare for a counter-offensive” ahead of the rumoured Russian advance.
“I have faith that the year 2023 can be the year of military victory,” he said, adding that Ukraine’s forces “cannot lose the initiative” they have achieved in recent months.
The defence minister was in France to strike a deal to purchase additional MG-200 air defence radars, which he said would “significantly increase the capacity of the armed forces to detect air targets, including winged and ballistic missiles, and drones of various types”.
Mr Reznikov’s comments come as Ukrainian intelligence alleges that President Putin has ordered his forces to seize the Donbas before the end of spring.
But speaking on Monday, Nato Secretary-General Jens Stoltenberg warned that there were no indications that Mr Putin had limited his military goals to seizing eastern regions of Ukraine.
“That they are actively acquiring new weapons, more ammunition, ramping up their own production, but also acquiring more weapons from other authoritarian states like Iran and North Korea,” Mr Stoltenberg said.
“And most of all, we have seen no sign that President Putin has changed his overall goal of this invasion – that is to control a neighbour, to control Ukraine. So as long as this is the case, we need to be prepared for the long haul.”
Meanwhile, Ukraine’s Deputy Defence Minster Hanna Malyar said that intense fighting was continuing in the Donbas region, where Russian forces and Wagner Group mercenaries have been trying to take the town of Bakhmut.
“Russian troops are actively trying to reach the borders of Donetsk and Luhansk regions,” she wrote on the Telegram messaging app. “Our soldiers defend every centimetre of Ukrainian land,” she said.