KIEV / BALACLAVA: Ukraine mobilised for war on Sunday and Washington threatened to isolate Russia economically, after President Vladimir Putin declared he had the right to invade his neighbour in Moscow’s biggest confrontation with the West since the cold war.

“This is not a threat: this is actually the declaration of war to my country,” Ukraine’s Prime Minister Arseny Yatseniuk, head of a pro-Western government that took power when Russian ally Viktor Yanukovich fled last week, said in English.

Putin secured permission from his parliament on Saturday to use military force to protect Russian citizens in Ukraine and told US President Barack Obama he had the right to defend Russian interests and nationals, spurning Western pleas not to intervene.

Russian forces have already bloodlessly seized Crimea – an isolated Black Sea peninsula where Moscow has a naval base.

On Sunday they surrounded several small Ukrainian military outposts there and demanded that the Ukrainian troops disarm. Some refused, leading to standoffs, although no shots were fired.

All eyes are now on whether Russia makes a military move in predominantly Russian-speaking eastern Ukraine, where pro-Moscow demonstrators have marched and raised Russian flags over public buildings in several cities in the last two days.

Russia has staged war games with 150,000 troops along the land border, but so far they have not crossed. Kiev says Moscow is orchestrating the protests to justify a wider invasion. Ukraine’s security council ordered the general staff to immediately put all armed forces on highest alert. However, Kiev’s small and under-equipped military is seen as no match for Russia’s superpower might.

The Defence Ministry was ordered to stage a call-up of reserves – theoretically all men up to 40 in a country with universal male conscription, though Ukraine would struggle to find extra guns or uniforms for significant numbers of them.

US Secretary of State John Kerry condemned Russia for what he called an “incredible act of aggression” and threatened “very serious repercussions”.

“You don’t just, in the 21st century, behave in 19th century fashion by invading another country on a completely trumped-up pretext,” Kerry told CBS programme Face the Nation.

Kerry said Moscow still had a “right set of choices” to defuse the crisis. Otherwise, G8 countries and other nations were prepared to “to go to the hilt to isolate Russia”.

“They are prepared to isolate Russia economically. The rouble is already going down. Russia has major economic challenges,” he said. He mentioned visa bans, asset freezes and trade isolation as possible steps. A Kremlin spokesman declined to comment after Kerry’s remarks.

Ukraine’s envoy to the United Nations said Kiev would ask for international military support if Russia expanded its military action in his country.

EASTERN UKRAINE: With Russian forces in control of majority ethnic Russian Crimea, the focus is shifting to eastern swathes of Ukraine, where most ethnic Ukrainians speak Russian as a native language.

Those areas saw more demonstrations on Sunday after violent protests on Saturday, and for a second day pro-Moscow activists hoisted flags at government buildings and called for Russia to defend them. Kiev said Russia had sent hundreds of its citizens across the border to stage the protests.

Obama spoke to Putin for 90 minutes by telephone on Saturday after the Russian leader declared he had the right to intervene and quickly secured a unanimous ‘yes’ vote from his parliament.

The Kremlin said Putin told Obama Russian speakers were under threat from Ukraine’s new leaders, who took over after the pro-Russian president fled huge protests against his repression and rejection of a trade deal with the European Union.

Ukraine, which says it has no intention of threatening Russian speakers, has appealed for help to Nato, and directly to Britain and the United States, as co-signatories with Moscow to a 1994 accord guaranteeing Ukraine’s security.

Nato ambassadors met in Brussels to discuss next steps. Secretary General Anders Fogh Rasmussen accused Russia of threatening peace and security in Europe.—Reuters