A Russian ambassador had harsh words for Finland on Saturday, warning that the country would retaliate against the new member of the North Atlantic Treaty Organization (NATO) if nuclear weapons were placed on Finnish soil.

Finland is one of the newest European countries to join the military alliance, being officially welcomed into the fold in April 2023. The Nordic nation was spurred to seek membership by Russia’s invasion of Ukraine in February 2022 and its increased threats of aggression against other nations. Sweden is the latest country admitted to NATO for this reason, joining on March 7.

Both nations announced that they were considering applying for membership in May of 2022, only a few months after the start of the Russia-Ukraine war.

Russia has long viewed NATO as an antagonistic force, given the influence of founding members like the United States and the United Kingdom. NATO members are also obliged to provide military aid to other members in the event of an attack, meaning that Russia risks a much larger conflict should it take action against the likes of Finland.