The European Union on Friday condemned an agreement between Russia and Belarus to allow the deployment of Russian nuclear warheads in Belarus.
"This is a step which will lead to further extremely dangerous escalation," EU foreign policy chief Josep Borrell said in a statement.
Russia moved ahead on Thursday with its plan to deploy tactical nuclear weapons in Belarus, whose leader said the warheads were already on the move. The plan was announced by Russian President Vladimir Putin in March.
On Thursday, Russian Defence Minister Sergei Shoigu said he was signing documents in Minsk on the process for storing such weapons in Belarus.
Borrell said the decision contravened multiple international agreements.
"We call on Russia to abide by these commitments," he said.
"The Belarusian regime is an accomplice in Russia's illegal and unprovoked war of aggression against Ukraine," Borrell added.
"We call on Belarusian authorities to put an immediate end to their support of Russia's war of aggression against Ukraine, and reverse decisions that can only contribute to heightening tensions in the region, and undermine Belarus' sovereignty."
He said any attempt "to further escalate the situation will be met by a strong and coordinated reaction".
