While Montenegro's Prime Minister Dusko Markovic visited Washington on Monday for a ceremony marking the country’s accession to NATO, Russia’s foreign ministry issued a stark warning over the move. “In the light of the hostile course chosen by the Montenegrin authorities, the Russian side reserves the right to take retaliatory measures on a reciprocal basis. In politics, just as in physics, for every action there is an opposite reaction,” the ministry said in a statement. The ministry also denounced the country’s “anti-Russian hysteria” and said it bore “full responsibility” for its policies after joining EU sanctions against Russia in 2014. Although no specifics were provided on the possible retaliatory measures, Moscow has previously threatened to target Montenegro’s tourism industry, which attracts many Russian visitors. Markovic also met with Vice President Mike Pence at the White House on Monday, though not with President Trump, who famously pushed Markovic out of the way to claim a spot front and center for a group photo at last week’s NATO summit, angering some Montenegrins. The incident appeared to be all but forgotten during Markovic's Washington visit, with the State Department welcoming Montenegro’s accession to the alliance and noting that it was accomplished “in the face of concerted foreign pressure.” U.S. Under Secretary of State Thomas Shannon said the nation “should be commended ... for asserting its sovereign right to choose its own alliances” despite disapproval from Moscow.