Kyiv (Ukraine) (AFP) – Finland on Thursday took a step towards fast-track membership of NATO, triggering a blunt warning from the Kremlin, as the war in Ukraine throttled supplies of Russian gas to Europe.

“Finland must apply for NATO membership without delay,” President Sauli Niinisto and Prime Minister Sanna Marin announced in a statement in Helsinki.

“NATO membership would strengthen Finland's security,” they said. “As a member of NATO, Finland would strengthen the entire defence alliance.”

But Kremlin spokesman Dmitry Peskov warned Russia would “definitely” see Finnish membership as a threat.

The Russian foreign ministry said Moscow would be “forced to take reciprocal steps, military-technical and other, to address the resulting threats to its national security.”

In launching the invasion of Ukraine, President Vladimir Putin cited in part what he called the threat from NATO, which expanded eastwards after the Cold War.

The foreign ministry accused NATO of seeking to create “another flank for the military threat to our country”.

“Helsinki should be aware of its responsibility and the consequences of such a move,” it said. 

Finland has been a declared neutral in East-West crises for decades, and as recently as January its leaders ruled out NATO membership of the alliance.

But the February 24 invasion shocked the Nordic nation.

It shares a 1,300-kilometre (800-mile) border with Russia and its past is studded with conflict with its giant neighbour.

NATO has already declared it will warmly embrace two countries with rich pockets and advanced militaries. 

Finland's entry will be “smooth and swift,” NATO chief Jens Stoltenberg promised on Thursday.

A special committee will announce Finland's formal decision on a membership bid on Sunday. 

Sweden, another neutral state, is widely expected to follow its neighbour. 

Russian gas

Russia's flow of gas to Europe gas fell meanwhile, spurring fears for Germany and other heavily-dependent economies.

Russian energy giant Gazprom announced it would stop supplying gas via the Polish part of the Yamal-Europe pipeline following retaliatory sanctions that Russia announced against Western companies on Wednesday.

Gazprom also said Thursday gas transiting to Europe via Ukraine had dropped by a third — a fall it blamed on Ukraine's pipeline operator, which the company denies and lays on Russia.

Ukraine and Poland are major supply routes for Russian gas to Europe and the two sides have kept flows going despite the conflict.

The European Union's heavy reliance on Russian energy has made it reluctant to add oil and gas imports to sanctions that are inflicting a toll on Russia's economy.

Germany accused Russia of using “energy as a weapon”.

“The situation is coming to a head,” Economy Minister Robert Habeck said.

The EU is struggling to overcome Hungarian resistance for plans to ban Russian oil.

Mykhailo Podolyak, a senior aide to Ukrainian President Volodymyr Zelensky, drew a parallel with the 1930s as he urged the bloc to impose an immediate embargo.

“If the leaders had acted decisively in 1938, Europe could have avoided WWII,” he wrote on Twitter. 

“But politicians acted cowardly and flirted with the aggressor. The result is million tragedies. History won't forgive us if we make the same mistake again.”

Shelling

Fighting in Ukraine has been concentrated on the south and east since Russia abandoned attempts to seize the capital Kyiv in the opening weeks of the war.

Ukraine's presidency said shelling continued throughout Lugansk — part of the Donbas region where Ukrainian forces are fiercely opposing Russian armour and Kremlin-backed separatists.

Russian troops are trying to take complete control of Rubizhne, block a key highway between Lysychansk and Bakhmut highway and seize Severodonetsk, the office said.

In the northeastern region of Chernigiv three people were killed and 12 others wounded early Thursday in a strike on a school in Novgorod-Siversky, the emergency services said. 

Across Ukraine, lives have been turned upside down, forcing millions to make anguished choices of how to respond.

Zhanna Protsenko, a social worker in the frontline town of Orikhiv, spoke to AFP as she was about to head off on her bicycle to visit people who refused or were unable to evacuate.

“How can I leave them here?” the 56-year-old asked, standing near a hospital that was hit by a strike in the past week. 

“We work. We have no time to hide,” she said as contractors repaired rows of the hospital's blown-out windows and an oil drum-sized hole blasted in its brick facade. 

War crimes

The UN Human Rights Council, in a session snubbed by Russia, was due to vote Thursday on a draft resolution calling for an investigation into war crimes.

“These have been 10 weeks of sheer horror to the people of my country,” Deputy Foreign Minister Emine Dzhaparova told the meeting from Kyiv.

“Only the world standing strong in solidarity with the Ukrainian people can defeat this pure evil.”

The invasion has sparked an exodus of nearly six million civilians, many of whom bear accounts of torture, sexual violence and indiscriminate destruction.

The Ukrainian prosecutor's office said it has received reports of more than 10,000 alleged crimes, with 622 suspects identified.

On Wednesday, the office said it would launch the first trial for war crimes.

Vadim Shishimarin, a 21-year-old Russian soldier, is accused of killing an unarmed 62-year-old civilian as he fled with four other soldiers in a stolen car.

In the southern port city of Mariupol, besieged troops in the vast Azovstal steelworks have been holding out against weeks-long bombardment, refusing demands to surrender.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said “negotiations are under way” about the situation there, focusing on a step-by-step operation beginning with the evacuation of the seriously wounded.

“There are hundreds of soldiers and officers of the armed forces, the national guard, the national police, security service, the border service and the defence forces,” she said.

“The guys need to be rescued. Everyone needs rescue.”