Ukraine's acting Foreign Minister said his country is ready to negotiate with Russia over the future of Crimea.

"I think there are signs for hope," Andriy Deshchytsa told reporters Saturday in Kiev.

Mr. Deshchytsa said Ukraine is working with other countries on setting up a "contact group" with Russia and it has made direct appeals to the Russian leadership. He said, however, the process is "fragile" and so far the Russians have not responded.

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Asked why he felt there were signs of hope, Mr. Deshchytsa said Ukraine had managed to pass on messages to the Russians and he believed they are considering the idea.

Mr. Deshchytsa reiterated his country's position that the March 16 referendum in Crimea is illegal and the results will be invalid. But he gave no indication Ukraine can do much about the vote beyond protesting and he could not say what plan Kiev has for its soldiers stationed there.

He also said Ukrainians will cope if Russia cuts off gas supplies. People will look for alternative sources of fuel, he said, such as wood.

Russian President Vladimir Putin rebuffed U.S. President Barack Obama's version of an hour-long call between the two, saying "relations should not be sacrificed due to disagreements over individual – albeit extremely significant – international problems."

In a phone conversation with U.S. Secretary of State John Kerry on Friday, Russian Foreign Minister Sergei Lavrov warned "hasty and reckless steps" could harm Russian-American relations, the foreign ministry said.

"Sanctions … would inevitably hit the United States like a boomerang," it added.

Even as Moscow and Washington moved military assets, both insisted they wanted a peaceful outcome.

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"There is a way to resolve the situation diplomatically, which addresses the interests of Russia, the people of Ukraine and the international community," Mr. Obama told his Russian counterpart according to the White House version of the phone call.

The military moves – on both sides – seemed carefully calibrated to demonstrate resolve rather than escalation toward confrontation. Each was carefully announced and each announcement was couched with assurances the moves were routine, not threatening.

As if to underscore that the crisis wasn't spinning out of control, Mr. Obama headed to Florida for some warmth away from still-chilly Washington.

Mr. Obama and his wife, Michelle, walked hand-in-hand Friday morning to Marine One, the presidential helicopter on the south lawn of the White House, leaving their teenage daughters behind as they left for the weekend.

Still, the risk of accidental confrontation remained as militaries postured and exercised.

For the second time in less than a week, Turkey sent warplanes to intercept a Russian spy plane patrolling offshore in international air space.

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Turkey, the pivotal nation in the confrontations between Russia and the Western powers, was coping with twin crises on its borders: the Syria civil war and the Ukrainian-Russian showdown over Crimea.

On Friday, the warship USS Truxton, a powerful destroyer carrying dozens of cruise missiles, passed through Turkey's Bosphorus Straits and headed for the Black Sea.

The Pentagon said the voyage wasn't a response to the Crimean crisis, but rather a long-scheduled exercise with Romanian and Bulgarian naval vessels.

Another warship, the frigate USS Taylor, remains in a Turkish port after running aground during a deployment to provide security patrols off Sochi during last month's Olympic Games.

In western Russia, a new round of war games for air-defence units got under way.

"Every day … the risk of military escalation increases," said Samantha Power, the U.S. envoy to the United Nations.

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In Lithuania on Thursday, six more U.S. F-15 warplanes flew in from the Lakenheath air base in Britain, bolstering the four F-15s already deployed to the tiny Baltic state as part of rotating air-defence patrol on NATO's forward frontier that now abuts Russia.

Mr. Putin claimed Moscow only intervened because Ukrainian fascists were threatening the ethnic Russian majority in Crimea and staged a coup against Viktor Yanukovych, the democratically elected ousted president of Ukraine.

In Moscow, a huge crowd gathered near the Kremlin at a government-sanctioned rally and concert billed as being "in support of the Crimean people."

Also Friday, military observers from the Organization for Security and Co-operation in Europe (OSCE) have been unable to enter the Crimea Peninsula for the second consecutive day, Reuters reported.

"Military assessment visitors from OSCE States denied entry into Crimea on Friday, heading back to Kherson to plan next steps," the organization posted on Twitter.

Over Sevastopol Bay, a pair of Hind helicopter gunships flew orbits, a potent reminder of Russia's military might on the peninsula that is still home to Moscow's Black Sea fleet and – for centuries – the key warm water, year-round, port for Russia's navy.