NATO members Poland and the Baltic states will seal off their borders with Russia’s ally Belarus in the event of any military incidents or a massive migrant push by Minsk, the interior ministers warned Monday.

The ministers said they were seeing growing tensions on NATO’s and the European Union’s borders with Belarus, which has taken in thousands of Russia’s military mercenaries and is pushing Middle East and African migrants into Europe, despite barriers having been put up.

They warned of swift and concerted reaction in the case of a military incident or large migrant push.