Thousands of ethnic Russians, who form the majority in Ukraine's Crimea region, demonstrated for independence for the peninsula that hosts part of Moscow's Black Sea Fleet yesterday. They scuffled with rival demonstrators, mainly from the Tatar minority, who support the new authorities in Kiev.
Moscow also denounced what it described as the rise of "nationalist and neo-fascist sentiment" in the country's mainly Ukrainian-speaking western areas, where it said Russian speakers were being deprived of rights. It has repeatedly expressed concern for the safety of Russian citizens in Ukraine.
Russian Defence Minister Sergei Shoigu said: "In accordance with an order from the president of the Russian Federation, forces of the Western Military District were put on alert."
Since Mr Yanukovich's downfall on Saturday, all eyes have been on Mr Putin, who ordered an invasion of neighbouring Georgia in 2008 to protect two self-declared independent regions with many ethnic Russians, which he then recognised as independent states.
Any military action in Ukraine would be far more serious - arguably the closest the West and Russia have come to outright confrontation since the Cold War.
Meanwhile, the International Monetary Fund has said it is prepared to send a team of negotiators to Kiev but a government must first be formed there and request the aid. US Deputy Secretary of State William Burns, visiting Kiev, said American financial experts were already in the country looking for ways to help.
Mr Yanukovich fled his luxurious palace on the outskirts of Kiev on Friday night after days of violence in which scores of his countrymen were killed, including demonstrators shot dead by police snipers from rooftops.
His downfall, three months after he abruptly turned his back on a free trade pact with the EU to seek closer ties with Russia, has infuriated Moscow, which describes the new authorities as extremists who seized power through force with the aid of Western powers.
Ukraine has suffered an identity crisis throughout two decades of independence from the Soviet Union. With borders drawn by Bolshevik commissars, it is split between a largely Ukrainian-speaking west, including areas annexed by the Soviets from Austria and Poland, and eastern provinces where Russian is spoken, mainly Russian territory since the Middle Ages.
In the Crimean regional capital Simferopol, pro-Russian crowds, some of them cossacks in silk and lambswool hats, shouted: "Crimea is Russian!" Mainly ethnic Tatar demonstrators backing the new authorities rallied under a pale-blue flag shouting: "Ukraine! Ukraine!"
Oleskander Turchinov, the parliament speaker who assumed the presidential duties after the assembly removed Mr Yanukovich from power on Saturday, took the helm of the armed forces yesterday.
He disbanded the riot police units blamed by the public for posting sharpshooters on rooftops who killed protesters. Mr Yanukovich's precise whereabouts are not known,