Reuters, Kiev :Ukraine mobilized 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,” Ukrainian Prime Minister Arseny Yatseniuk said in English. Yatseniuk heads a pro-Western government that took power in the former Soviet republic when its Moscow-backed president, Viktor Yanukovich, was ousted last week.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.Financial markets reacted to the escalating tensions when trading opened in Asia on Monday, with oil and wheat futures jumping and stock indexes falling.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 the Ukrainian troops disarm. Some refused, leading to standoffs, although no shots were fired.As Western countries considered how to respond to the crisis, the United States said it was focused on economic, diplomatic and political measures, and made clear it was not seriously considering military action.US Secretary of State John Kerry will visit Kiev on Tuesday to show “strong support for Ukrainian sovereignty, independence, territorial integrity, and the right of the Ukrainian people to determine their own future, without outside interference or provocation”, the State Department said in a statement.The Group of Seven major industrialized nations, condemning the Russian intrusion into Ukraine, suspended preparations for the G8 summit that includes Russia and had been scheduled to take place in June in Sochi, site of the recent Winter Olympics.Finance ministers from the G7 said they were ready to offer “strong financial backing” to Ukraine, provided the new government in Kiev agreed to pursue economic reforms sought by the International Monetary Fund.Analysts said US economic sanctions would likely have little impact on Russia unless they were paired with strong measures by major European nations, which have deeper trade ties with Moscow and are dependent on Russian gas.But EU officials said the European Union was unlikely to match the United States in threatening sanctions against Russia when its foreign ministers meet to discuss Ukraine on Monday, instead pushing for mediation between Moscow and Kiev.