The US said on May 18 it is confident Finland and Sweden will become part of NATO, despite vocal Turkish protests – an expansion that would dramatically realign European security in the wake of Russia’s military offensive in Ukraine.

Reflecting the brutality of the conflict which has reinvigorated the transatlantic alliance, Ukraine held its first war crimes trial since Moscow poured troops across the border beginning February 24, with a 21-year-old Russian soldier pleading guilty to the cold-blooded murder of a Ukrainian civilian.

The launch of Kyiv’s judicial reckoning over alleged atrocities committed on its soil after 12 weeks of war and thousands of deaths came as President Vladimir Putin was forced to confront the vexing prospect of NATO sharply expanding its reach on his borders.

Abandoning decades of non-alignment, Finland and Sweden formally submitted a joint application to join the military alliance at its headquarters in Brussels.

Throwing America’s full weight behind the Nordic nations, President Joe Biden said he “strongly” backs their NATO bid and offered US support in the event of “aggression” during the application process.

In a sign of Washington’s resolve to stand firm with Ukraine, the US reopened its embassy in Kyiv after a three-month closure, with employees raising the Stars and Stripes in a modest ceremony.

Biden’s comments came one day before he was to welcome Finnish President Sauli Niinisto and Swedish Prime Minister Magdalena Andersson to the White House for meetings set to underscore the strategic reach of their decision.

Reacting to the NATO applications, British Prime Minister Boris Johnson said they would not have been expected a short time ago, “but Putin’s appalling ambitions have transformed the geopolitical contours of our continent”.

The accession bid faces stiff resistance from NATO member Turkey, which accuses the Nordic neighbours of harbouring anti-Turkish extremists.

President Recep Tayyip Erdogan demanded “respect” from NATO over his government’s concerns.

But Western allies remain optimistic they can overcome Turkey’s objections. For now, several including Britain have offered security guarantees to the Nordic nations to guard against any Russian aggression.

“We’re confident that at the end of the day Finland and Sweden” will enter NATO and “that Turkey’s concerns can be addressed,” US National Security Advisor Jake Sullivan said.

In an effort to lower the diplomatic heat, US Secretary of State Antony Blinken met at the United Nations Wednesday with Turkey’s Foreign Minister Mevlut Cavusoglu, who called the face-to-face discussion “extremely positive.”

On the ground, in Ukraine’s ruined port city of Mariupol more than 1,000 Ukrainian soldiers including senior commanders remained inside the besieged Azovstal steel plant, a pro-Russian separatist leader said.

Moscow said 959 of the troops had surrendered this week.

Kyiv’s defence ministry pledged to do “everything necessary” to rescue the personnel still in the sprawling plant’s tunnels but admitted there was no military option available.

Those who have left the heavily shelled Azovstal plant were taken into Russian captivity, including 80 who were seriously wounded, Russia’s defence ministry said.

The ministry, which published images showing soldiers on stretchers, said the injured were transported to a hospital in the eastern Donetsk region controlled by pro-Kremlin rebels.

The defence ministry in Kyiv said it was hoping for an “exchange procedure... to repatriate these Ukrainian heroes as quickly as possible”.

But their fate was unclear, with Kremlin spokesman Dmitry Peskov refusing to say whether they would be treated as criminals or prisoners of war.

Putin had “guaranteed that they would be treated according to the relevant international laws”, Peskov said.

Russia’s alleged disregard for international law has played out in Ukraine with accusations – including mass rape and massacres – that are under investigation by international bodies.

Ukraine’s President Volodymyr Zelensky hit out at Moscow in his nightly address to the nation, calling Russia’s offensive an “absolute failure” and saying the once-mighty military has nearly exhausted its missile stockpile.

“They are afraid to acknowledge that catastrophic mistakes were made at the highest military and state level,” Zelensky said.