Ukraine leader issues 'three hour' Crimea ultimatum

Ukraine announced plans Wednesday to drop out of a key post-Soviet alliance and slap entry visas on Russians while also preparing for a possible Crimean withdrawal following the Kremlin's absorption of the peninsula.

Kiev's first firm response to Russia's claim to the strategic Black Sea peninsula came as a deadline expired on an ultimatum set by the acting president for Crimea's separatist leaders to release the captured head of the Ukrainian navy.

The spiralling crisis prompted the White House to warn Russia it was "creating a dangerous situation" and the NATO commander to call the Kremlin's seizure of Crimea "the gravest threat to European security and stability since the end of the Cold War".

Germany said it was suspending a major arms deal with Moscow -- a signal that Washington's EU allies were willing to take more serious punitive steps against the Kremlin despite their heavy dependence on Russian energy supplies.

But Moscow appeared ready to up the diplomatic stakes, warning Washington it was preparing a "wide range" of countermeasures should the United States follow through on threats to impose broad economic sanctions.

Pro-Russian forces earlier seized two Crimean navy bases and detained Ukraine's naval chief as Moscow tightened its grip on the flashpoint peninsula despite Western warnings that its "annexation" would not go unpunished.

Dozens of despondent Ukrainian soldiers -- one of them in tears -- filed out of Ukraine's main navy headquarters in the historic Black Sea port city of Sevastopol after it was stormed by hundreds of pro-Kremlin protesters and masked Russian troops.

The local prosecutor's office said Ukraine's navy commander Sergiy Gayduk -- appointed after his predecessor switched allegiance in favour of Crimea's pro-Kremlin authorities at the start of the month -- had been detained.

Russian Defence Minister Sergei Shoigu later urged Crimea's pro-Russian leaders to free Gayduk, but only after the expiry of a 9:00 pm (1900 GMT) deadline set by Ukraine's acting president Oleksandr Turchynov for the Crimean authorities to release the commander.

Read more: Ukraine leader issues 'three hour' Crimea ultimatum - Yahoo News