Ukraine’s acting president warned Russia to keep military personnel confined to their naval base after suspected pro-Russian gunmen seized a regional government headquarters and parliament in the Crimea region, NBC News reported. Acting Ukrainian President Olexander Turchinov said any military movements would “be seen by us as military aggression.” The comments also came after Russian armored personnel carriers and trucks carrying troops were seen this week on the streets of Sevastopol, the Crimean city about 500 miles south of Kiev where the Russian Black Sea fleet is based. Defense Secretary Chuck Hagel told a NATO press conference on Thursday that he's "closely watching" Russia's military exercises along the Ukrainian border and warned Russia "not to take any steps that could be misinterpreted, or lead to miscalculation during a very delicate time."