Nato doubled down on Tuesday on its commitment to one day include Ukraine, a pledge that some officials and analysts believe helped prompt Russia’s invasion this year. The world’s largest security alliance also pledged to send more aid to Ukrainian forces locked in battle with Russian troops.

US secretary of state Antony Blinken met with Nato foreign ministers in Romania to drum up support for Ukraine as Russia bombards energy infrastructure ahead of the frigid winter.

Russia cannot stop the alliance’s expansion, Nato leaders said. “Nato’s door is open,” Nato secretary-general Jens Stoltenberg said before chairing the meeting in Bucharest. He highlighted that North Macedonia and Montenegro had recently joined Nato, and said that Russian President Vladimir Putin “will get Finland and Sweden as Nato members” soon.

The Nordic neighbours applied for membership in April, concerned that Russia might target them next.

“Russia does not have a veto” on countries joining, Stoltenberg said.

“We stand by that, too, on membership for Ukraine.” When they met in Bucharest in 2008, Nato leaders said that Ukraine and Georgia would join the alliance one day.