Russia threatened to deploy nuclear weapons in and around the Baltic Sea region if Finland and Sweden join the North Atlantic Treaty Organization as tensions fueled by President Vladimir Putin’s invasion of Ukraine spread.

“In this case, there can be no talk of non-nuclear status for the Baltic,” Dmitry Medvedev, deputy chief of Russia’s Security Council and former president, said in a Telegram post Thursday, suggesting Russia may deploy Iskander missiles, hypersonic weapons and nuclear-armed ships in the region.

Medvedev’s comments are among the most detailed threats Russia has issued over the prospect that its northwestern neighbors might join the alliance after decades of staying out. But both Finland and Sweden this week said they’re stepping up consideration of the issue in the wake of Russia’s invasion of Ukraine.

But Lithuanian President Gitanas Nauseda dismissed the threats as “empty,” accusing Russia of already placing tactical nuclear weapons in the Kalinigrad exclave on the Baltic. “I don’t know if one can deploy something anew that’s already been deployed,” Nauseda told a press conference in Vilnius.

Russia based Iskander missiles, which can carry both nuclear and conventional warheads, in Kaliningrad starting in 2018, according to the Center for Strategic and International Studies, a Washington think tank. Moscow has never publicly confirmed that.

Kremlin spokesman Dmitry Peskov declined to comment on the possibility nuclear weapons might be deployed in the Baltic region but said that Putin has already ordered the military to prepare plans for boosting defenses along Russia’s western frontiers.

Medvedev said he hoped that “reason” would prevail and the countries would decide not to join the alliance.

Russia’s border with Finland runs for over 1,300 kilometers (800 miles), which is more than the total length of its frontier with current NATO members. If the countries join the alliance, “we will need to seriously strengthen our land forces and anti-aircraft and deploy substantial naval forces in the Gulf of Finland basin,” Medvedev said.

Though the initiatives to consider NATO membership picked up in both countries only after the invasion, Medvedev said Russia’s move wasn’t to blame. At the same time, he suggested that while keeping Ukraine out of the western alliance was a key goal of Russia’s operation there, the Kremlin sees the situation with Finland and Sweden region differently.

“We don’t have territorial disputes with those countries like we do with Ukraine,” he said. “For that reason, the price of their membership for us is different.”

Bloomberg