The call came amid growing anxiety among Kiev's Western-backed rulers that Russian President Vladimir Putin - flushed with expansionist fervour - will imminently order an all-out attack on his ex-Soviet neighbour after only being hit by limited EU and US sanctions for taking the Black Sea cape.
"The aim of Putin is not Crimea but all of Ukraine," Ukraine's National Security and Defence Council chief Andriy Parubiy told a mass unity rally in Kiev.
"His troops massed at the border are ready to attack at any moment," he said a day after Russian forces used armoured personnel carriers and stun grenades to capture Ukraine's main Crimean airbase.
The takeover came as the chill in East-West ties grew stiffer with a charge by Germany -- a nation whose friendship Putin had nurtured -- of a Kremlin attempt to "splinter" Europe along Cold War-era lines.
Europe's most explosive security crisis in decades will now dominate a nuclear security summit opening in the Hague tomorrow that will include what may prove the most difficult meeting to date between US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov.
The encounter comes with Russia facing the loss of its coveted seat among the G8 group of leading nations and Putin's inner circle reeling from sanctions Washington unleashed for their use of force in Crimea in response to last month's fall of Ukraine's pro-Kremlin regime.
One of the biggest tests facing the besieged Western-backed leaders in Kiev now comes from restless Russians who have been stirring up violent protests and demanding their own secession referendums in the southeastern swaths of Ukraine.
The region's mistrust of the new team's European values lies from cultural and trade ties with Russia that in many cases are centuries old -- a fact seized upon today by Crimea's self-declared prime minister.
Sergei Aksyonov said in an impassioned address he posted on Facebook and read out on local TV that Crimea began facing a "sad fate" the moment three months of deadly protests involving a mix of nationalist and pro-Western forces toppled the pro-Kremlin regime in Kiev.
But we resisted and won! Our motherland -- Russia extended her hand of help," said Aksyonov. "So today, I appeal to you with a call to fight."
"I call on you to resist the choice made for you by a bunch of political mavericks who are being financed by oligarchs."
Aksyonov said he was "deeply convinced" that the future of southeastern Ukraine "rested in a close union with the Russian federation -- a political, economic and cultural union".
Crimea's rebel authorities estimate they together with the Kremlin's forces control at least half of Ukrainian bases on the Black Sea peninsula and about a third of its functioning naval vessels.
The most dramatic episode of Russia's excursion so far saw crack forces break into the Belbek airbase near the main city of Simferopol after an armoured personnel carrier blasted through the main gate.
Two more armoured personnel carriers followed and gunmen stormed in firing automatic weapons into the air. An AFP
reporter heard stun grenades before the situation calmed and
the gunmen lowered their weapons.
Several of the base's unarmed soldiers began singing the Ukrainian national anthem during the ensuing lull. Ukraine's interim President Oleksandr Turchynov said Sunday that the Russian forces had captured the base's commander Yuliy Mamchur, and demanded his immediate release.
"We are demanding an end to this aggression against Ukraine and its citizens," Turchynov said in a statement. But Russia's Deputy Defence Minister Anatoly Antonov denied his forces were conducting "any military activities that could threaten the security of neighbouring states".
But Russia's diplomatic isolation is growing as quickly as the reemergence of an ideological divide that appeared to have been bridged with the 1989 fall of the Berlin Wall. Germany -- whose economic power is playing a decisive role in forging Europe's response to Putin's increasingly belligerent stance -- warned after talks with Ukraine's leaders that the continent's future was at stake. "The referendum in Crimea... is a violation of international law and an attempt to splinter Europe," Foreign Minister Frank-Walter Steinmeier told reporters after meeting Ukrainian Prime Minister Arseniy Yatsenyuk.
The show of diplomatic solidarity may play an important psychological role in Kiev as it faces new pressure from
Russia that include open threats to throw Ukraine's wheezing
economy into convulsion by raising its gas rates and demanding
colossal payments for disputed debts it could ill afford.
Yet Ukraine is unlikely to hear its calls for US and EU military support answered. Yatsenyuk said he and Steinmeier had discussed
"military and technological cooperation assistance" for Ukraine's vastly underfinanced and outdated force of 130,000 soldiers -- a fraction of Russia's 845,000 troops.
Both the United States and Europe have thus far limited their retaliation against Putin to targeted travel and financial sanctions that concern officials but do not impact the broader Russian economy.
Washington's steps have been more meaningful because they hit what US officials call a Putin "crony bank" as well as oligarchs who are believed to be closest to the Russian strongman and -- in one case -- actually running a joint business with him.
Leading EU nations such as Britain and Germany their financial and energy sectors intertwined with Russia's have questioned why they should suffer most in case of an all-out trade war.