Russia and Ukraine both held military exercises on November 24 amid rising tensions prompted by reports of a large Russian military buildup near the Ukrainian border that raised fears of a possible invasion.
Russia staged military drills in the Black Sea, south of Ukraine, saying it needed to sharpen the combat-readiness of its conventional and nuclear forces because of what Defense Minister Sergei Shoigu called 'the growing activity of NATO countries near Russia's borders.'
During the Black Sea drills, Russian warplanes and ships practiced repelling air attacks on naval bases and responding with air strikes, Interfax reported.
Ukraine, meanwhile, staged exercises of its own near its northern frontier, which it said were meant to beef up preparedness for a potential spillover of a monthslong migrant crisis on the border between European Union member Poland and Belarus.
Kyiv and its Western backers have raised alarm bells in recent weeks over a Russian military buildup near Ukraine, whose military intelligence chief claimed on November 21 that Russia has amassed 92,000 troops near its borders and was readying an attack for early February.
The Kremlin has called such allegations "groundless."
Shoigu on November 23 complained that U.S. bombers had rehearsed a nuclear strike on Russia, coming too close the Russian border, drills the Pentagon said had adhered to international protocols.
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Russia seized Ukraine's Crimean Peninsula in March 2014, and has been backing separatists in eastern Ukraine in an ongoing conflict that has claimed more than 13,200 lives since April 2014.
The United States and NATO have reaffirmed their support for Ukraine including through warship maneuvers this month in the Black Sea and a delivery of U.S. patrol boats to the Ukrainian Navy.
Ukraine's Border Guard Service, meanwhile, held what it called a 'special operation' at the border with Belarus on November 24, including drone exercises and military drills for anti-tank and airborne units amid concerns that a migrant crisis at the Polish-Belarusian frontier could spill into Ukrainian territory.
The service said in a statement that the operation is part of measures to 'increase the protection and defense of the Ukrainian border in order to prevent a migration crisis and combat illegal activities.'
The operation was conducted jointly with the National Guard, the National Police, and the Armed Forces, the service said.
Volodymyr Nikiforenko, the deputy head of the Border Guard Service, said the main task of the operation was to prevent illegal migrants from crossing the state border and entering Ukraine.
Kyiv has also voiced worries that the border with Belarus, a close Russian ally, could be used by Russia to stage a military assault.
Ukraine has deployed 8,500 troops and police officers to guard its border with Belarus, aiming to prevent possible attempts by migrants to breach the frontier.
It also said some of its airborne units carried out paratrooper jumps in the southern Mykolayiv region, near the country's main seaport of Odesa and Russian-occupied Crimea.
Amid the rising tensions in the region, the U.S. and Russian top military officers spoke over the phone on November 23.
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General Valery Gerasimov, chief of the Russian General Staff, and General Mark Milley, chairman of the U.S. Joint Chiefs of Staff, discussed 'current questions of international security,' Russia's Defense Ministry said in a statement on November 23.
The U.S. Department of Defense confirmed the call, saying in a statement that Gerasimov and Milley discussed 'security-related issues of concern.'
The Russian Defense Ministry and the Pentagon did not provide further details.
With reporting by Reuters and AP
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