Finland's president has signed a 10-year security deal with Ukraine in Kyiv where President Volodymyr Zelenskiy says he believes Russia planned to mobilise 300,000 new troops for its war by June.
The pact signed by President Alexander Stubb and Zelenskiy made Finland the eighth NATO member this year to commit to long-term security co-operation and defence backing for Ukraine as it battles to hold back Russian forces.
Ukraine has signed similar agreements with the United Kingdom, Canada, Denmark, France, Germany, Italy and the Netherlands.
Finland, which shares a 1340km border with Russia, joined NATO a year ago.
Stubb said Finland would also send 188 million euros ($A310 million) in additional military aid, including air defences and heavy-calibre ammunition.
That sum took Finland's overall defence contribution to about 2 billion euros during the war.
"We are not giving this military support only for Ukraine to defend itself, we are giving this military support for Ukraine to win this war," Stubb told a joint news conference in Kyiv.
Ukraine relies heavily on foreign air defence systems and has faced a recent surge in Russian missile and drone attacks that have battered its energy system.
On the battlefield, Ukraine is on the back foot as military assistance from the United States stalls and Ukrainian troops find themselves outgunned by a larger and better armed foe.
Russia has inched forward.
Although he provided no evidence to back up his assertion, Zelenskiy told the news conference: "I can say that Russia is preparing to mobilise 300,000 military personnel by June 1."
Russian President Vladimir Putin denied in December that there was a need to conduct another wave of mobilisation, something that would be politically sensitive.
On Wednesday, the Russian defence ministry said more than 100,000 people had signed contracts with the army since the start of the year, including about 16,000 in the past 10 days following a deadly attack on a concert hall near Moscow.
Zelenskiy's comments come as the Ukrainian parliament considers a closely watched overhaul of the rules governing how Ukrainian civilians are called up into the army to fight for their country.
This week, Zelenskiy signed legislation reducing the draft age to 25 from 27, expanding the number of people who can be called up to fight.
At the news conference, he said he did not think Ukraine needed to mobilise as many as 500,000 more people into the army - an idea he floated late last year - but that he did not know yet how many were needed.
Separately Russian drones hit residences in Kharkiv, Ukraine's second largest city, killing three rescue workers, the mayor and the regional governor said.
Kharkiv regional Governor Oleh Synehubov, writing on the Telegram messaging app, said the rescue workers were killed early on Thursday after they had arrived at the scene of the attack and a new strike occurred.
He said a total of four strikes had hit the city and the top floors of one apartment building had been damaged.
Kharkiv Mayor Ihor Terekhov said one strike had triggered a fire. Part of another building had collapsed.
Reuters was unable to independently verify the accounts.
Kharkiv has been a frequent target of Russian drone and missile attacks.
with DPA
