Vladimir Putin has hit out at what he called Nato’s “imperial ambitions” after the military alliance cleared the way for Sweden and Finland to join.
Mr Putin warned the two countries that if “military contingents and military infrastructure” were deployed there, “we would be obliged to respond symmetrically”.
He told reporters in Turkmenistan: “Ukraine and the wellbeing of Ukrainian people is not the aim of the collective West and Nato but a means to defend their own interests.
“The Nato countries' leaders wish to... assert their supremacy, their imperial ambitions”.
Nato branded Russia the biggest “direct threat" to Western security after its invasion of Ukraine on Wednesday and vowed further support for Kyiv.
Leaders of the alliance pledged that from 2023 there would be a seven-fold increase in combat forces on high alert along its eastern flank against any future Russian attack.
Among the new commitments was a pledge by Britain to provide an extra £1bn of military support to Ukraine, a near doubling of its commitment to Ukrainian military aid.
US President Joe Biden also announced more land, sea and air force deployments across Europe from Spain in the west to Romania and Poland bordering Ukraine.
This included a permanent army headquarters with a battalion in Poland - the first full-time US deployment on Nato’s eastern fringe.
“President Putin's war against Ukraine has shattered peace in Europe and has created the biggest security crisis in Europe since the Second World War," Nato Secretary-General Jens Stoltenberg told a news conference.
“Nato has responded with strength and unity," he said.
Russia intensified its attacks in Ukraine in the wake of the Nato summit, including with missile strikes and shelling on the southern Mykolaiv region.
The mayor of Mykolaiv city said a Russian missile had killed at least five people in a residential building there.
Moscow claimed its forces had hit what it called a training base for foreign mercenaries in the region.
The governor of eastern Luhansk province also reported “fighting everywhere" in a battle around the hilltop city of Lysychansk, which Russian forces are trying to encircle in their bid to capture the industrialised eastern Donbas region.
