Finland on Saturday sought to allay Moscow’s fears about its bid to join NATO, as fierce fighting raged in Ukraine’s east, slowing a Russian advance.

Wives and parents of Ukrainian fighters trapped in the bowels of a besieged steel plant in the country’s south meanwhile made a desperate appeal to China to help secure their release.

And the wealthy countries of the G7 vowed to further turn the screw on the Kremlin with fresh sanctions, pledging never to recognise the borders it is attempting to redraw through destructive force.

One of Europe’s fiercest conflicts since World War II has seen more than six million people flee for their lives, and according to Kyiv has caused an estimated $90 billion in damage to civilian infrastructure.

US Defence Secretary Lloyd Austin urged his Russian counterpart Sergei Shoigu to move immediately to implement a ceasefire, in their first talks since before the conflict began on February 24.

But one senior Ukrainian general predicted a turning point in the months ahead, and said the fighting could be over by the end of the year.

Finland and Sweden are poised to jettison decades of military non-alignment to join NATO as a defence against feared further aggression from Russia.

Moscow has warned Finland, with whom it shares a 1,300km border, that it would take “reciprocal steps”.

Finland’s grid operator said Russia halted electricity supplies overnight, though Finnish officials said power supplied by Sweden had made up for the losses.

Ahead of talks with NATO members in Berlin, Finnish Foreign Minister Pekka Haavisto said he was “confident that in the end we will find a solution and Finland [and] Sweden will become members of NATO”.

Earlier, in a phone call initiated by Helsinki, President Sauli Niinisto had a “direct and straightforward” conversation with Russian president Vladimir Putin.

“Avoiding tensions was considered important,” Niinisto’s office said.

Putin, however, told him that Finland joining NATO would be a “mistake”, insisting that Russia posed “no threat to Finland’s security”, the Kremlin said.

Finland’s bid to join NATO is expected to be announced over the weekend.

Finland and Sweden will first have to win over NATO member Turkey on the sidelines of the informal gathering of the alliance’s foreign ministers in Berlin.

Turkish President Recep Tayyip Erdogan on Friday said he opposed their membership bids and accused both countries of harbouring “terrorist organisations”.

Both Nordic countries have sizable Kurdish populations. Ankara has regularly accused Stockholm in particular of harbouring members of the separatist Kurdistan Workers’ Party (PKK), which has been designated a terrorist organisation in the UK, EU and the US.

It has also been angered by Sweden’s assertion that the mass killings of Armenians under the Ottoman Empire between 1915 and 1917 constituted genocide.

But Turkey on Saturday expressed readiness at least to discuss Finnish and Swedish membership.

“A big majority of the Turkish people are against the membership of those countries who are supporting PKK terrorist organisation,” Foreign Minister Mevlut Cavusoglu said upon arrival for the Berlin talks.

He added, however, that “these are the issues that we need to talk, of course, with our NATO allies as well as these countries.”