Ukraine told Russia that a military invasion would be an act of war following a vote by lawmakers in Moscow to give President Vladimir Putin the right to send troops after pro-Russian forces seized control of Crimea.

Ukraine, which put its military on full combat alert, is also mobilizing the reserves, Andriy Parubiy, secretary of the National Security and Defense Council, said in a briefing today. He urged the U.S. and U.K. to defend the country’s territorial integrity. Putin told U.S. President Barack Obama that Russia may act if violence spreads to Russian-speaking regions, the Kremlin said in a statement.

In a 90-minute phone call, Obama “expressed his deep concern over Russia’s clear violation of Ukrainian sovereignty and territorial integrity” and told Putin his country is violating international law by sending troops into Ukraine, according to a White House statement.

The U.S. and Canada are suspending preparations for a meeting of the Group of Eight industrial nations in Russia in June. The U.S. called on Russia to withdraw its forces to bases in Crimea, refrain from interfering elsewhere in Ukraine and conduct “direct engagement” with the country’s newly formed government.

Facing Default

Ethnic strife erupted in Ukraine’s Crimea region, where the majority of the population is Russian, after an uprising led to last week’s overthrow of President Viktor Yanukovych. The military movements risk destabilizing the country as its new government looks to the U.S. and Europe for a bailout to avoid default.

“The Ukrainian state will protect all citizens no matter in which region they live in and which language they speak or which church they attend,” acting Ukrainian President Oleksandr Turchynov said.

Tensions in the mostly Russian-speaking Crimea have worsened since gunmen took control of the regional legislature this week and installed a pro-Kremlin premier, Sergey Aksenov.

Ukraine asked the European Union, the U.S. and the North Atlantic Treaty Organization to consider “all means’ for the defense of its territorial integrity, the Interfax news service reported, citing Foreign Minister Andriy Deshchystya.

The United Nations Security Council held an emergency session to discuss the events in Ukraine. Following a request from Poland, NATO’s North Atlantic Council will meet today for consultations on a potential threat to its security.

‘Act of Aggression’

In a statement to the Security Council, Ukrainian Ambassador to the UN Yuriy Sergeyev called on the international community ‘‘to do everything possible” to stop a Russian “act of aggression,” saying the number of Russian soldiers in Crimea is increasing “every hour.”

Russian UN Ambassador Vitaly Churkin said “cooler heads should prevail” and the West must stop spurring the conflict by encouraging protesters.

U.S. Ambassador to the UN Samantha Power called for observers and told the session that Russia approving the use of force is “dangerous and destabilizing.”

Canada is recalling its ambassador to Moscow, Prime Minister Stephen Harper said in a statement. Japanese Foreign Minister Fumio Kishida said his country is concerned about the situation and urged all parties to exercise restraint.

‘Back Off’

“People right around the world will be thinking right now: hands off the Ukraine,” Australian Prime Minister Tony Abbott said today, according to an e-mailed transcript of an interview on Channel 10’s “The Bolt Report.” “This is not the kind of action of a friend and neighbor and really, Russia should back off.”

Crimea was given to Ukraine by Russia in 1954 by then-Soviet leader Nikita Khrushchev. Ethnic Russians comprise 59 percent of Crimea’s population of about 2 million people, with 24 percent Ukrainian and 12 percent Tatar, according to 2001 census data. Russians make up 17 percent of Ukraine’s entire population of 45 million people.

Heeding a request by Putin to protect ethnic Russians, lawmakers in Moscow yesterday voted unanimously to allow him to send troops to its neighbor after unidentified troops seized facilities in Ukraine’s southern Crimea region.

‘Naked Aggression’

Ukraine is diverting funds for the military, Yatsenyuk said. Putin had no reason to request the use of force against Ukraine as Russians aren’t under threat, Turchynov said.

Turchynov earlier accused Russia of “naked aggression.” Ukraine’s defense minister said yesterday that Russia has sent 6,000 more soldiers into Crimea in the past 24 hours, while Crimean Premier Sergey Aksenov, who asked Russia for help, said Russian troops were guarding key buildings there, Interfax news service reported.

“The situation is under control,” Aksenov, who had asked for aid from Russia and was voted as leader in a closed-door session after gunmen took control of the legislature this week, was quoted as saying by Interfax. “Cooperation has been established with the Black Sea Fleet on guarding crucial facilities.”

A U.S. official described events over the past days as an orchestrated series of steps intended to make Russian military intervention in Crimea appear legitimate. The official requested anonymity to discuss classified intelligence matters.

‘Tyranny and Violence’

Putin has not yet made a decision on when to send troops, his spokesman Dmitry Peskov said by phone. Ukraine’s government said efforts to speak with Russia’s Foreign Ministry were ignored.

The vote by Russian lawmakers followed an appeal by the council of Russia’s State Duma to protect Russians in Crimea from “tyranny and violence,” RIA Novosti reported, citing SpeakerSergei Naryshkin.

Lawmakers also said Russia should no longer abide by a 1994 agreement under which Ukraine gave up its nuclear weapons in exchange for a guarantee from the U.S., U.K. and Russia to protect its independence and territorial integrity.

Russia’s Foreign Ministry said gunmen “sent by Kiev” tried to seize Crimea’s Interior Ministry. An unidentified group of masked men also took over the trade union building in Crimea’s capital, Simferopol.

Gunmen earlier surrounded Crimea’s main airport in the capital, while more than 10 trucks carrying Russian servicemen encircled the Kirov military airfield, Interfax reported, citing an unidentified person in the Ukrainian military.

Pro-Russian protesters yesterday stormed the chamber of the regional government in Kharkiv, a city in Ukraine’s northeast, and ejected government supporters in clashes where both sides threw stones and wielded sticks, the Unian news service reported yesterday.

Moscow’s Orbit

Russia has alarmed Western leaders with moves in Crimea to thwart any push by Ukraine’s democratic movement to draw the nation toward the European Union and out of Moscow’s orbit.

The turmoil comes as Ukraine’s new government tries to shore up an economy in need of aid. Ukraine needs $15 billion in the next 2 1/2 years from the International Monetary Fund, and securing a deal at the start of April would be the best scenario, Finance Minister Oleksandr Shlapak said in Kiev yesterday.

It wasn’t clear what tools the U.S. and its allies have to deter Russia from escalating the situation.

“There could be trade or financial sanctions on Russia,” said Daniel Serwer, senior fellow at the Center for Transatlantic Relations at the Johns Hopkins School of Advanced International Studies in Washington. “The problem is no one wants to go back to a Cold War.”

Russian Goal

A full invasion of Ukraine could risk interrupting deliveries of Russian gas to other European nations and further destabilizing a country that’s already on the brink of default and elected a new government only this week. Gazprom yesterday reiterated that Ukraine owes $1.55 billion for supplies of Russian gas, RIA said, citing company officials.

Putin’s goal may instead be to ensure Russia’s military dominance of the region survives through its hold on the deep-water Black Sea port of Sevastopol, which it received in a leasing deal with Ukraine until 2042. The threat of military force may set the stage for a referendum slated for March 30 in Crimea over whether the region should have more independence from Kiev, said Ruslan Pukhov, director of the Moscow-based Center of Analysis of Strategies and Technologies.

“What the Russian army is doing now is guaranteeing the impossibility for Kiev to use force in Crimea and to ensure that the referendum will be passed,” Pukhov said by phone yesterday. “Putin’s goal is to have Crimea with as wide rights of autonomy as possible and become de facto Russia’s unofficial protectorate. The plan is to keep the Black Sea fleet forever.”

To contact the reporters on this story: Daryna Krasnolutska in Kiev atdkrasnolutsk@bloomberg.net; Volodymyr Verbyany in Simferopol, Ukraine atvverbyany1@bloomberg.net

To contact the editors responsible for this story: Balazs Penz at bpenz@bloomberg.net; John Walcott at jwalcott9@bloomberg.net Alaa Shahine, Andrew J. Barden