Fistfights broke out between rival demonstrators in the Crimea region of Ukraine yesterday as Russian President Vladimir Putin ordered major military exercises just across the border.
The tests of military readiness involve most of the units in central and western Russia, Defence Minister Sergei Shoigu said in a televised statement.
He said the exercise would "check the troops' readiness for action in crisis situations that threaten military security".
In Kiev, opposition leaders who took charge after pro-Russian President Viktor Yanukovych fled were working on forming a new government to chart a path forward for the country and its ailing economy.
Parliament has delayed the announcement of the new administration, which was originally set for Tuesday, reflecting the political divisions among the factions of the opposition. When announcing Russia's military exercises, Shoigu didn't specifically mention the turmoil in Ukraine, which is bitterly divided between pro-European western regions and pro-Russian areas in the east and south.
Three months of protests forced Yanukovych to go into hiding over the weekend as his foes set up an interim government after violent clashes between protesters and police that left more than 80 dead.
In Crimea's regional capital of Simferopol, about 20,000 Muslim Tatars who rallied in support of the interim government clashed with a smaller pro-Russian rally.
One health official said at least 20 people were injured, while the local health ministry said one person died from a heart attack.
The protesters shouted and attacked each other with stones and bottles and traded punches, as police and leaders of both rallies struggled to keep the two groups apart.
They started to disperse after the speaker of the regional legislature said it would postpone a crisis session, which many Tatars feared would have taken steps towards seceding from Ukraine.
"The threat of separatism has been eliminated," Refat Chubarov, leader of the Tatar community in Crimea, told the crowd.
Crimean Tatars are a Turkic Muslim ethnic group who have lived in Crimea for centuries.
They were brutally deported in 1944 by Soviet dictator Josef Stalin, but returned after Ukraine's independence.
The tensions in Crimea - a peninsula in southern Ukraine that is home to Russia's Black Sea Fleet - highlight the divisions that run through the country.
They also underscore fears that the mainly Russian-speaking east and south won't recognise the legitimacy of the interim authorities.
"Only Russia can defend us from fascists in Kiev and from Islamic radicals in Crimea," said Anton Lyakhov, a 52-year-old pro-Russian protester.
According to the Russian defence minister, the military will be on high alert for two days.
The actual manoeuvres will start tomorrow and will last four days, he said. The exercise will involve ships of the Baltic and Northern fleets and the air force. The order came a day after a Russian lawmaker visiting Crimea said Moscow would protect the region's Russian-speaking residents, raising concerns that Russia might make a military move into Ukraine.
Nato Secretary-General Anders Fogh Rasmussen said: "We take it for granted that all nations respect the sovereignty and independence and territorial integrity of Ukraine, and this is a message that we have also conveyed to whom it may concern."
Yesterday, Yanukovych's three predecessors as president issued a statement accusing Russia of "direct interference in the political life of Crimea".
Russian officials categorically denied any plans to move militarily on Ukraine.
"That scenario is impossible," said Valentina Matvienko, speaker of the upper chamber of Russia's parliament. She is a close Putin ally and was born in western Ukraine.
"Russia has been reiterating its stance that we have no right to interfere in the domestic affairs of a sovereign state," she said. "We are for Ukraine as a united state, and there should be no basis for separatist sentiments."