US troops have been sent to Bulgaria as part of NATO operations to support Eastern European countries from potential aggression by Russia. The move is the last one in a series of multinational training and security cooperation activities.

This move comes at a tenuous time in the relationship between Russia and the fledgling administration of President Trump, who voiced unusually strong support for NATO. One hundred twenty troops from Fort Carson, Colorado, arrived Wednesday at the Novo Selo training range in eastern Bulgaria.

US combined-arms battalions with some 4,000 soldiers are moving to Estonia, Latvia, Lithuania, Poland, Romania, Hungary and Bulgaria. This campaign began in response to Russia's meddling in Ukraine in 2014 and its annexation of Crimea. 

NATO operations are disliked by Russia

Moscow has criticized the deployments, calling them provocative and a threat to Russia. Vladimir Putin reiterated that position at the annual board meeting of the Federal Security Service. He said that Russia was declared the main threat to NATO for the first time since 1989, and that the alliance stated that containing Russia is its new mission. 

Putin declared that they are provoking us constantly and are trying to draw us into confrontation. NATO is seen as dangerous by many Russian politicians and people.

US leaders opinions on NATO and Russia

Trump has questioned NATO's importance, although last week he committed to attend a May meeting of NATO leaders in Europe. US Defense Secretary James Mattis described Russia's actions around the world as destabilizing and aggressive.

Mattis added that we are not in a position to collaborate on the military level in this moment, but our political leaders will try to find common ground. US Secretary of State Rex Tillerson stated on Thursday that US will consider working with Russia when practical but will stand up for US and allies' interests when both nations disagree.