Nato will show President Vladimir Putin he gets the opposite of what he wants when he behaves aggressively towards another nation by hastily accepting Finland and Sweden into the military family, the treaty's chief Jens Stoltenberg said.
The two countries have expressed a strong interest in signing up to the 30-member transatlantic treaty since Russia invaded Ukraine in late February.
Addressing young leaders at the Nato Youth Summit in Brussels on Thursday, Mr Stoltenberg, the alliance’s secretary general, said if Finland and Sweden launched attempts to join, the accession process would be speeded up. This, he suggested, would deal a significant blow to Mr Putin’s efforts to intimidate the alliance by starting a war on its frontier.
“It’s for Finland and Sweden to decide and Nato will respect their decision regardless. That’s exactly the opposite of what Russia does, they try to intimidate and threaten countries to do what Russia wants,” Mr Stoltenberg said.
“If the condition is that they apply, then we will welcome them with open arms.
“I strongly believe the accession process can go very quickly.
“It will demonstrate to President Putin that he gets exactly the opposite of what he wants. He invaded Ukraine because Nato was on his borders and what he gets is more Nato.”
In a tweet posted on Thursday, Mr Stoltenberg said Finnish President Sauli Niinisto had updated him on "deliberations in Finland on potential Nato membership".
Before launching the war in Ukraine, Mr Putin demanded that Nato stop expanding and pull its troops back from Russia’s borders. So the prospect of neighbouring Finland, and Sweden, joining the transatlantic alliance is unlikely to be welcomed in Moscow.
Finland has a conflict-ridden history with Russia with which it shares a 1,340 kilometre border. A recent poll of Finns showed 84 per cent believe Moscow poses a significant military threat.
Sweden has avoided military alliances for more than 200 years, choosing a path of peace after centuries of warfare with its neighbours.
Both countries put an end to traditional neutrality by joining the European Union in 1995 and deepening co-operation with Nato. However, a majority of people in the two countries were firmly against full membership in the alliance – until now.
Finnish and Swedish leaders have yet to announce a final decision on whether they wish to join Nato.
The issue of their potential membership is expected to feature heavily at the Nato summit in Madrid in June.
Since Mr Putin invaded Ukraine, Sweden has stepped up security and remilitarised the island of Gotland, which is key to stability in the Baltic Sea.
About 40,000 troops from Nato countries are stationed across the Baltic states as well as Poland and Romania, which share borders with Ukraine.
Addressing about 100 young adults at the youth summit in Brussels, as well as hundreds more who were watching online, Mr Stoltenberg warned of the dangers of taking peace in the post-Cold War era for granted.
“Young people in Nato-allied countries today have not experienced war,” he said. While he acknowledged this was a positive point he said “it’s also dangerous” because if countries take peace for granted it could easily lead to “mistakes that create the conditions for war”.
The Nato chief said the alliance would continue with its campaign of putting “maximum pressure” on Moscow, which includes sanctions, to deter its ambitions to take over Ukraine.
He also said member states are prepared to continue arming the Ukrainians in the long term in the hope of helping them to oust the invaders.
“We will continue to put maximum pressure on President Putin to end the war,” he said. “We need to be prepared for the long term. It’s a very unpredictable and fragile situation in Ukraine but there’s absolutely the possibility that this war will drag on and last for months and years.”
Mr Stoltenberg said Nato nations that supply Kyiv with weaponry through bilateral agreements are committed to upgrading Ukrainian military equipment from Soviet-era devices to more modern and sophisticated pieces.
Turning to the issue of climate change, Mr Stoltenberg said it is crucial for Nato to tackle because it will avert conflicts.
“Climate change fuels conflict, conflict fuels war and therefore it matters for Nato.”
At the beginning of the summit, a vote of participants showed the youngsters perceive the spread of disinformation to be the biggest challenge to global security. Asked what the most powerful tool for combating this is, Mr Stoltenberg said a free and independent press.
