In yet another troubling sign for America’s tense relations with Russia, U.S. intelligence officials say Putin has began construction on new nuclear-proof underground bunkers.

Russia began building ‘dozens’ of underground bunkers across the country several years ago, the Washington Free Beacon reported citing US officials.

The U.S. and Russia have been working together to get rid of their nuclear weapons since the end of the Cold War, but the revelation coupled with Russia’s recent surge in missile production suggests they are preparing for conflict.

‘Russia is getting ready for a big war which they assume will go nuclear, with them launching the first attacks,’ Mark Schneider, a former Pentagon nuclear policy official told the Free Beacon. ‘We are not serious about preparing for a big war, much less a nuclear war.’