Russia deployed thousands more troops and military hardware near the Ukrainian border Thursday, as Western governments stepped up diplomatic pressure aimed at defusing the international standoff over Ukraine's future.
The Russian deployment came as Ukraine's interim Prime Minister Arseniy Yatsenyuk told the United Nations Security Council that Russian military "aggression" in and near his country is undermining global security. He described that military presence in his country as having "no reasons and no bounds."
For her part, U.S. Ambassador Samantha Power called for "a climate of restraint," and for "peaceful dialogue to replace [Russian] coercion."
Moscow, which sent thousands of military personnel into Ukraine earlier this month, is backing a referendum Sunday that was called to decide whether Crimea should secede from Ukraine and possibly join the Russian Federation.
U.S. and European leaders accuse Russia of interfering in Ukraine's internal affairs. They say the vote is illegal and have threatened Moscow with economic and diplomatic sanctions if Crimea leaves.
In a statement Thursday, acting Ukraine President Oleksandr Turchynov warned that the Russian forces massed near the border appear "ready to intervene at any time."
Russian media say the new maneuvers will take place over the next two weeks.
Earlier this week, NATO announced its own deployment of fighter jets and surveillance aircraft in European territories bordering Russia.
In Washington, Secretary of State John Kerry testified at a U.S. Senate hearing, reiterating the U.S. position that the referendum violates the constitution of Ukraine, as well as international law and the charter of the United Nations. He estimated Russia may have 20,000 troops in Crimea.
Kerry and his Russian counterpart, Sergei Lavrov, are set to discuss Ukraine Friday at a face-to-face meeting in London.
In her address to the Security Council, U.S. Ambassador Power accused Russia of pursuing a course of military action "from the outset" of the crisis, which erupted in full in late February when pro-Russian President Viktor Yanukovych -- facing weeks of anti-government protests -- fled the country.
She also accused Moscow of supporting pro-Russian efforts inside Crimea "to take control of Ukrainian border posts, and to "surround Ukrainian military facilities."