KIEV (AFP) - Rallies were planned across Ukraine on Sunday as the troubled ex-Soviet state struggled to contain upheaval amid a standoff between Russia and the West over Crimea that shows no sign of easing.
Sunday marks 200 years since the birth of Ukraine's national hero, the poet Taras Shevchenko, and patriotic rallies were planned in Kiev and - in a show of defiance of Russia's de facto control over Crimea - the peninsula's key cities of Simferopol and Sevastopol.
Pro-Russian protesters were due to hold a counter-rally in the tense eastern city of Donetsk, where clashes were feared between them and pro-Kiev demonstrators also planning to celebrate Shevchenko.
The internal wrangling over Ukraine's identity and future were mirrored on the international stage by escalating hostilities between Russia and the West.
Pro-Kremlin militia fired warning shots on Saturday to stop foreign observers from entering Crimea, and Moscow threatened to suspend its participation in nuclear arms monitoring deals.
It was the third straight day that civilian and military observers from the Organisation for Security and Co-operation in Europe (OSCE) tried and failed to enter the Black Sea peninsula to check on the standoff between overpowered Ukrainian troops and a mass of Russian forces and Kremlin-backed militias.
Forty gunmen in balaclavas and military fatigues fired shots above the OSCE convoy of 54 civilian and military observers from 29 of the organisation's member countries.
The OSCE monitoring mission is an instrumental part of a three-pronged diplomatic push by US President Barack Obama that also includes a call for Russia to pull its Crimean troops back to their barracks and Ukraine to hold early presidential polls in May.
Ukraine's border guards service added to the tinderbox atmosphere by reporting that one of its light patrol planes had come under fire from "extremists" in the same area but escaped unscathed.
They also accused Russia of seizing a ferry terminal and a navy yard in the east and southwest of Crimea to send convoys of 67 military transport trucks filled with soldiers toward Simferopol, the capital of the region, whose parliament has voted to secede and hold a March 16 referendum on joining Russia.
The 19th-century poet Shevchenko has been credited with creating the modern Ukrainian language and the idea of Ukraine as a nation, and the anniversary of his birth gives the new government in Kiev a powerful occasion for nation-building at a time when the country is threatening to splinter.
Ukraine, a culturally divided ex-Soviet nation of 46 million people, has been in upheaval since three months of deadly unrest brought new, pro-European leaders to power last month and sent ousted president Viktor Yanukovych into hiding in Russia.
Sunday's rally in Kiev will be held in a park dedicated to Shevchenko, before a concert in Independence Square, the heart of the anti-Yanukovych protests.
Interim president Oleksandr Turchynov and prime minister Arseniy Yatsenyuk will take part in the rally beneath a statue of Shevchenko, whose bushy moustache and frowning eyes peer out from similar monuments in almost every Ukrainian town.
The Kremlin accuses Ukraine's new rulers of fomenting an atmosphere of intimidation against the Russian speakers who make up the majority of Ukraine's southeast.
That has prompted President Vladimir Putin to threaten to use force - a shock decision that has sparked the worst East-West crisis since the Cold War.
Russia says it has stepped up protection of its Black Sea Fleet base in Crimea and is working together with "local self-defence units", but refuses to acknowledge deploying extra troops.
But Ukrainian Border Guards General Mykola Kovil said there were now 30,000 Russian soldiers in Crimea - 5,000 more than the contingent allowed under a deal with Kiev on the Black Sea Fleet base.
Russia's decision to flex its military muscle has prompted Washington to announce visa bans and asset freezes on Moscow officials and halt various forms of military cooperation.
The European Union has also threatened to toughen economic sanctions against Russia.
In response, a Russian defence official said Moscow may halt foreign inspections of its vast nuclear arsenal carried out under the 2010 Strategic Arms Reduction Treaty (START) - a highlight of Obama's diplomacy - and a 2011 OSCE deal.
Russian state-run energy giant Gazprom has also threatened to cut off gas shipments to debt-laden Ukraine over unpaid bills - a move that would almost certainly affect the firm's western European clients.
The military standoff and diplomatic wrangling have also translated into an information war. Western and Ukrainian journalists have been threatened by Crimean gunmen and the peninsula has replaced broadcasts from several television channels based in Kiev with Russian ones.
Britain's BAE Systems defence and security company reported that Ukraine has been stricken by a powerful computer virus whose likes have not been seen since the Stuxnet malware programme wreaked havoc on Iran's uranium enrichment system in 2010.
The British defence group said a code in the virus suggested it was created in the same timezone as Moscow.