Ukrainian President Petro Poroshenko has warned he would not hesitate to impose martial law and mass troops if necessary in response to the military build-up by Russia near the border region. He said if the Crimea situation deteriorates, mobilisation of Kiev's army will be announced soon.

"In the event of the exacerbation of the situation in the east and in Crimea [...] we will have to impose martial law and order mobilisation," Poroshenko told a gathering, reports Kiev's Unian news agency.

Russia's Deputy Defence Minister General Dmitry Bulgakov said the country's forces are engaged in logistics and material support exercises in Crimea.

"The logistics support units embarked on working out the practical tasks of logistics support in the naval and land ranges of the Republic of Crimea," he said.

Tens of thousands of Russian troops have been positioned in the newly set up military installations, which are within striking distance of Ukraine.

Tensions between Ukraine and Russia have sharply escalated in recent weeks in the border region, primarily centred on Crimea, a former Ukrainian territory which became part of Russia in 2014.

Analysts say Russia's latest deployment is in line with its military strategy to keep a close watch on Ukraine, a west-inclined neighbour.

"Russia's plans around the Ukrainian border show a real intent to use force if needed. They would be Russia's first line of assistance if the pro-Russian rebels in east Ukraine needed help," Anton Lavrov, a defence analyst at Moscow-based think tank CAST, told the Wall Street Journal.

Ukraine's security agencies in the border region report that Russia has placed as many as three reconnaissance systems meant for electronic warfare near the border. A large number of tanks and ammunition supplies have also been spotted in the troubled regions of Donetsk and Lugansk, reports Ukraine Today.

President Vladimir Putin had earlier accused Ukrainian forces of killing two Russian service personnel in the region. Though Kiev had denied the accusation calling it an aggression by Moscow, the Russian president said he would consider counter-terror measures in the region.