Nicaragua on Tuesday shrugged off the idea of Russia building a military resupply base in this Central American nation after a suggestion last week by the Russian defense chief.

In Ukraine, pro-Kremlin forces are in de facto control of the strategic, majority-Russian Crimean peninsula, where Ukrainian troops remain blocked inside their barracks in the most serious stand-off between the West and Russia since the end of the Cold War.

EU foreign policy chief Catherine Ashton held "useful" talks in Madrid Tuesday with Russian Foreign Minister Sergei Lavrov over the spiraling crisis in Ukraine, a European source said.

"We had a useful discussion which lasted over an hour," a European diplomatic source quoted Ashton as saying after the meeting held in the Russian ambassador's residence in Madrid.

Russian President Vladimir Putin has calmed fears of an imminent war between Russia and Ukraine's new authorities but also made clear that Moscow has no intention of loosening its new grip on Crimea in defiance of Western anger.

Breaking an uncharacteristic silence since the downfall of president Viktor Yanukovych 10 days ago, Putin on Tuesday displayed no fear of a prolonged crisis in ties with the West over the situation in the Ukrainian region of Crimea which is now controlled by pro-Moscow forces.

Ukraine's 150,000 ethnic Hungarians, feared as potential fifth columnists for ousted president Viktor Yanukovych, face a growing threat from far-right nationalists.

In the region of western Transcarpathia, the large Hungarian minority has grown increasingly uneasy.

NATO will hold a meeting with the Russian ambassador to the U.S.-led military alliance on Wednesday, just one day after a second emergency gathering on the Ukraine crisis.

"There will be an NRC (NATO-Russia Council meeting) tomorrow at ambassadorial level. We expect it will take place in the afternoon," a NATO spokesman said Tuesday.

Two Russian warships crossed Turkey's Bosphorus Strait early Tuesday headed towards the Black Sea, Turkish media reported.

The reported ship movements came with Russia and the West locked in a standoff over Ukraine's Crimean peninsula on the Black Sea.

Russian Foreign Minister Sergei Lavrov said Tuesday that threats of sanctions against Moscow are counter-productive and will not change its position on the Ukraine crisis.

"Our position is honest and... will not change," Lavrov told a news conference in Tunisia, where he was on an official visit.

President Vladimir Putin denied on Tuesday that Russian troops were operating in the Ukrainian Black Sea region of Crimea, while sending Moscow's forces to Ukraine would be an entirely legitimate move but also a last resort.

U.S. President Barack Obama, however, said Putin's rationale for his incursion into Crimea was not "fooling anybody" and said Russian "meddling" would push states away from Moscow.

Ukraine Prime Minister Arseniy Yatsenyuk will meet EU leaders Thursday ahead of an emergency summit the same day on the crisis in his country, EU President Herman Van Rompuy said.

EU leaders "will discuss situation in Ukraine with PM Yatsenyuk in Brussels Thursday prior to extraordinary summit," Van Rompuy said in a Tweeted message Tuesday.

Russia could reduce to zero its economic dependency on the United States if Washington agreed sanctions against Moscow over Ukraine, a Kremlin aide said on Tuesday, warning that the American financial system faced a "crash" if this happened.

"We would find a way not just to reduce our dependency on the United States to zero but to emerge from those sanctions with great benefits for ourselves," said Kremlin economic aide Sergei Glazyev.