Ukrainian military spokesman Vladislav Seleznyov said the commander of the Ukrainian navy, Admiral Serhiy Haiduk, was driven away by what appeared to be Russian special forces. Ukrainian servicemen defend the entrance of the Ukrainian navy headquarters in Sevastopol, Crimea, on Wednesday. Crimea's so-called self-defence forces on Wednesday stormed the Ukrainian navy headquarters in the Black Sea port of Sevastopol. Credit:AP In Kiev, acting President Oleksander Turchinov threatened to take action if pressure on Ukrainian forces in Crimea did not stop. "If by 2100 all provocations against Ukrainian troops have not stopped and Admiral Haiduk and all other hostages ... are not released, the authorities will take appropriate measures, including of a technical and technological nature," he said in a statement posted online. Most of Crimea's electricity, water and food is supplied from the Ukrainian mainland and Mr Turchinov's comments suggest Kiev could be prepared to squeeze the supplies.

"The Russian military is cynically refusing to negotiate ending the provocations and releasing the hostages," Mr Turchinov said. Russia's Itar-Tass news agency reported that Alexander Vitko, commander of Russia's Black Sea Fleet which is based in Sevastopol, had been involved in talks at the headquarters. Shortly after the takeover of the base, Ukraine's acting Defence Minister Ihor Tenyukh said in Kiev that the country's forces would not withdraw from Crimea even though Russian President Vladimir Putin has signed a treaty to make it part of Russia. But an hour later, Ukrainian servicemen, unarmed and in civilian clothing, began walking out of the headquarters. Within a few minutes a handful of troops in Ukrainian uniform, looking shell-shocked at the dramatic turn of events, followed suit. Later, pro-Western Ukrainian Prime Minister Arseniy Yatsenyuk ordered his first deputy prime minister and acting defence minister Mr Tenyukh to fly to Crimea to "resolve the situation."

But Sergei Askyonov, Crimea's new prime minister since the Russian takeover, said Vitaly Yarema and Mr Tenyukh would not be permitted to land. Thousands of Russian soldiers took control of Crimea in the buildup to a weekend referendum last weekend in which the region, with ethnic Russians in the majority, voted overwhelmingly to leave Ukraine and join Moscow. Mr Putin said his move to take control of Crimea was justified by what he calls "fascists" in Kiev who overthrew pro-Moscow president Viktor Yanukovich last month after three months of violent street protests. Ukraine and Western governments have dismissed the referendum as a sham, and say there is no justification for Mr Putin's actions. Moscow officially denies deploying extra troops and Russian soldiers in the region are wearing unmarked uniforms, making it difficult to verify exactly who is who on the ground.

Syria More broadly, relations between the US and Russia over the crisis in Crimea worsened overnight after the US ordered Syria to close its US embassy. The Syrian Foreign Ministry condemned the action as a violation of international diplomatic conventions, in a statement carried by Syrian state television on Wednesday. Moscow called it "worrying and disappointing". The Russian Foreign Ministry suggested Washington's actions were aimed at "regime change" to oust Syrian President Bashar al-Assad whom Russia has protected at the UN Security Council and with arms deals.

"The aim of regime change in Damascus prevails over the task of disarming Syria of its chemical weapons and helping millions of Syrians who have suffered from the armed conflict," the ministry said on its website. Loading Syria announced on March 10 it would stop providing consular services in the United States. State Department officials said while embassy and consular activities were affected the United States was not severing diplomatic relations with Syria. Reuters