Russian troops, meanwhile, pulled up to the Ukrainian military base at Perevalne on the Crimean Peninsula in a convoy Sunday that included at least 13 trucks and four armored vehicles with mounted machine guns. The trucks carried 30 soldiers each and had Russian license plates.
In response, a dozen Ukrainian soldiers, some with clips in their rifles, placed a tank at the base's gate, leaving the two sides in a tense standoff. It appeared to be the first known case of outmatched Ukrainians standing up to Russian military might.
Unidentified soldiers were also seen cutting power to the headquarters of the Ukrainian Naval forces in Crimea — whose own commander defected later Sunday and pledged his allegiance to "the people of Crimea."
In Kiev, a Ukrainian security official said the head of the Ukrainian Navy — Adm. Denis Berezovsky — had been dismissed and faces a treason investigation after declaring his allegiance to the pro-Russian government of the Crimea region and offering no resistance to the Russian troops.
The speaker of Crimea's legislature, Vladimir Konstantinov, was quoted as saying local authorities do not recognize the new government in Kiev. He said a planned referendum on March 30 would ask voters about the region's future status.
A convoy of hundreds of Russian troops was also seen heading toward Simferopol, the regional capital of Crimea. Armed men in military uniforms without markings strolled around Simferopol's central plaza, Lenin Square, outside its Council of Ministers building.
"It is very important that we all do everything we can to calm tensions," said British Foreign Minister William Hague, who flew to Kiev on Sunday.
He said he has urged Russian officials to "speak directly to the Ukrainians" but so far they had not.
President Barack Obama talked with Putin by telephone for 90 minutes Saturday and expressed his "deep concern" about "Russia's clear violation of Ukrainian sovereignty." Obama warned that Russia's "continued violation of international law will lead to greater political and economic isolation."
In Moscow, at least 10,000 people bearing Russian flags marched freely through the city Sunday, while a few dozen demonstrating on Red Square against the invasion of Ukraine were quickly detained by Russian riot police.
"We understand that the West wants to attack us and seize this territory. It (the West) is dangerous to us," said Victor Sidelin, a Moscow resident at the march.