As Secretary of State John Kerry headed for embattled Kiev to meet with Ukraine’s fledgling leadership, President Vladimir V Putin on Tuesday described the crisis there as the result of an “unconstitutional coup,” throwing his support behind ousted President Viktor F Yanukovych and reserving the right to use force as “a last resort," news reports said.

In televised remarks reported by Reuters, Putin also said there was no need to use force at the moment in Crimea, Ukraine's southern region on the Black Sea where Russian troops and naval vessels have encircled Ukrainian military facilities, saying they were protecting ethnic Russians.

Putin’s remarks came after he declared the scheduled end of a surprise military exercise he ordered in western Russia near Ukraine’s border last week, telling military units that participated to return to their permanent garrisons. There was no indication that Putin’s move presaged any easing of a crisis that has raised Western fears that the region may be spinning toward a broader conflict. Tension remained high in Crimea where Russian troops are blockading Ukrainian military facilities in what the authorities in Kiev have called a declaration of war. Russia says its action is designed to protect ethnic Russians in Crimea.

In a graphic illustration of the standoff and its potential hazards, Russian troops on Tuesday fired warning shots in the air as around 200 unarmed Ukrainian soldiers approached Russian positions on the perimeter of the contested Belbek airfield in Crimea to press demands to return to their positions there and conduct joint patrols. Only when the Ukrainians were a matter of feet from Russians firing over their heads did the Ukrainians call a halt and a dozen of them were allowed through the Russian blockade to allow them to take up their former positions. The rest of the Ukrainian force remained outside.

In Moscow, the Kremlin responded to American warnings of economic punishment and isolation for its actions in Crimea with a counterthreat that Moscow might abandon the dollar as a reserve currency and refuse to repay loans to American banks, Reuters reported. The warning came from Sergei Glazyev, a Kremlin aide with limited influence over the formulation of a policy but boasting a reputation for staking out hard-line positions, the news agency said.

Kerry was expected to meet with the fledgling Ukrainian leadership that forced president Yanukovych to flee to Russia last month as the crisis deepened. He will be the highest-ranking Western official to meet the administration, signaling the Obama administration’s support for a government that the Kremlin does not recognise.

The Russian military exercise coincided with the deployment of Russian special forces troops to Crimea beginning last Friday, though officials maintained it was not directly related to the conflict in Ukraine. Nothing the Kremlin reported suggested that the Russian operations in Crimea would end.

The military exercise involved the mobilisation of the entire Western Military District, which stretches from the border of Ukraine to the Arctic, as well as units from the Central Military District, the Baltic Fleet and air defence commands. The troops dispatched to Ukraine are reported to have deployed from ports and airfields in the Southern Military District.

Palpable message

Putin ordered the mobilisation only days before Russian forces began spreading through Crimea, and despite officials’ reassurances to the contrary, the timing and scale of the operations had a palpable message. Putin attended the culmination of the exercises near St Petersburg on Monday, appearing in state television reports observing live-fire training involving tanks and helicopters.

The Kremlin announced the end of the manoeuvres – which involved 150,000 troops, as well as air and naval forces and live-fire demonstrations in several Russian bases – and reported that they had been “successfully carried out.” On Monday, the embattled new government of Ukraine accused Russian forces of a major escalation in military pressure over control of the Crimean Peninsula, saying Russia had deployed 16,000 troops in the region over the last week and had demanded that Ukrainian forces there surrender within hours or face armed assault.

Russia denied it had issued any ultimatum and no fighting was reported, but Moscow was clearly moving to strengthen its grip on Crimea, brushing aside new admonitions of economic punishment and isolation from President Obama and European leaders.

As Ukraine is tugged by the East and the West, many in Crimea welcome Russia’s aggressive stance, hoping Moscow will secure their place in a fractured future. At the United Nations, where the Security Council met for the third time in an emergency session since Friday, the Ukrainian ambassador, Yuriy Sergeyev, distributed a three-page letter asserting that the Russians had sent 16,000 troops into the Crimean Peninsula since Feb 24. The troops, Sergeyev wrote, had moved to “seize, block and control crucial governmental and military objects of Ukraine in Crimea.”

The Interfax-Ukraine news agency quoted an unidentified Ukrainian defence ministry official as saying that Russia’s Black Sea Fleet commander had set a deadline of 5 am Tuesday — 10 pm Monday, Eastern time — for Ukrainian forces stationed in Crimea to lay down their weapons, and that many Ukrainian soldiers seemed to have taken the threat seriously. Russia’s Interfax news agency said the Black Sea Fleet had no such plans, and the would-be deadline came and went, apparently uneventfully.

Still, the conflicting reports only served further to worsen tensions in the Ukrainian crisis, which has grown drastically in the past weeks to a new confrontation between Russia and the West reminiscent of low points in the Cold War.

Russia has denied Western accusations that it flouted international law in asserting military control in Crimea, a historically Russian region that is home to its Black Sea naval base. The Russians have asserted that they moved to protect their legitimate interests there after President Yanukovych fled more than a week ago after protests in Kiev against his shift toward closer relations with Russia.

The Kremlin still regards him as Ukraine’s legitimate president. The Security Council meeting in New York was requested by Russia’s ambassador, Vitaly I Churkin, who told fellow members that Russia had acted to thwart what he called threats by ultranationalists, including anti-Semites, against Russians and Russian speakers inside Ukraine. Churkin also held up a copy of a letter from Yanukovych to Russia asking for military help.

Yet the Security Council meeting quickly became a venue for East-West diplomatic gibes and rejoinders. The British ambassador, Mark Lyall Grant, called Russia’s justification bogus, while the envoy from Lithuania, Raimonda Murmokaite, told the Council it “resurrects the memory of darkest pages of the 20th century.”

The Council took no action, and it remained unclear what — if anything — it might agree to do, since Russia, a permanent member, has veto power. Although Crimea was relatively calm Russian forces tightened their grip on key military bases and other facilities throughout the peninsula, including naval installations and outposts of the border police, and stepped up pressure on Ukrainian officials to declare their loyalty to pro-Russian authorities.