Days after the ouster of Ukraine’s president Viktor Yanukovich, who was considered an ally of neighboring Russia’s, Russian troops were spotted in Sevastopol and another 150,000 soldiers put on high alert for war games near the Ukrainian border.

Canada’s The Globe and Mail newspaper reported on Wednesday that Russian military personnel had set up a checkpoint on the main highway that connects the Crimean capital Simferopol and Sevastopol, a city on the Black Sea coast that headquarters Russia’s Black Sea Fleet.

Russian defense minister Sergei Shoigu was quoted by the state news agency RIA as saying that the authorities in Moscow were “carefully watching what is happening in Crimea” and taking “measures to guarantee the safety of facilities, infrastructure and arsenals of the Black Sea Fleet.”

In recent days, thousands of ethnic Russians living in the Crimea have demonstrated for independence from Kiev where an interim government was formed over the weekend by Oleksandr Turchynov, the former parliamentary speaker. Yanukovich called the takeover a “coup d’état.”

The transition came after months of protests against Yanukovich’s shock decision late last year to scuttle a trade deal with the European Union and deepen ties with his country’s former Soviet master Russia instead. Especially in the western parts of Ukraine that were formerly part of the Austro-Hungarian Empire and Poland, people rebelled.

The Crimea, which was part of the Russian Empire for almost two centuries before Soviet leader Nikita Khrushchev transferred it to what was then the Ukrainian Soviet Socialist Republic in 1954, is mainly populated by ethnic Russians and a bastion of Yanukovich supporters. The former president is believed to be hiding there.

Ethnic Tatars, the indigenous population of the peninsula, look more favorably on events in Kiev. Most Tatars were deported to Central Asia by Joseph Stalin in 1944 on suspicion of collaborating with the Nazis. Tens of thousands returned after Ukraine gained its independence with the collapse of the Soviet Union in 1991. They are now a minority in what used to be their homeland.