Gunmen captured a military agency in the capital of Simferopol today, according to the private TV5 television station. Border guards said Russian soldiers stormed a unit near the Kerch Strait last night and seized weapons. As Putin presided over the opening ceremony of the 2014 Paralympic Games in Sochi yesterday, lawmakers in Moscow pledged to accept the results of a March 16 referendum on Crimea joining Russia.

Ukraine is struggling to keep hold of Crimea, home to Russia’s Black Sea Fleet, after pro-Russian forces took control of it in the wake of Moscow-backed Viktor Yanukovych’s ouster as president. Western officials say they’re concerned that the situation in the peninsula, where the U.S. estimates there now are 20,000 Russian troops confronting a smaller Ukrainian military force, could explode at any moment.

“Russia and Ukraine, right now, are one nervous 20-year- old soldier’s mistake away from something very, very bad happening that could spin out of control,” said Steven Pifer, a former U.S. ambassador to Ukraine. There are about 12,000 Ukrainian troops in Crimea, he said.

Base Stormed

Ukraine’s border guard service said in a statement that a division at Shcholkino was stormed by Russian soldiers, who beat servicemen, confiscated their mobile phones and forced them and their families to leave. Eleven border guard units are currently being blocked, according to a separate statement.

The service later said 100 Russian soldiers and 50 other men took control of the ferry across the Kerch Strait to Russia, stopping border guards from inspecting 31 trucks arriving in Crimea. The Defense Ministry reported yesterday that armed men had attacked and entered a Ukrainian base in Sevastopol. The men withdrew after talks, according to TV5.

Pifer said Russian forces have tried to provoke Ukraine’s military and that it was “very commendable” the Ukrainians haven’t challenged the Russians who’ve surrounded their bases.

“There needs to be some kind of de-escalation,” said Pifer, a senior fellow at the Brookings Institution, a Washington public policy research group.

Gunmen have blocked observers from the Organization for Security and Cooperation in Europe from entering Crimea to monitor events there for two days.

Cold War

The plan to determine Crimea’s status through a vote, which Ukraine’s new leaders and Western powers consider illegal and unconstitutional, heightens tensions in the worst dispute between Russia and the West since the end of the Cold War. Ukraine will do its best to resolve conflict in Crimea peacefully, Foreign Minister Andriy Deshchytsya said today.

U.S. President Barack Obama has urged Ukraine to control its military and avoid giving Russia a pretext to escalate with military force, said two U.S. officials who requested anonymity to discuss intelligence reports and diplomatic contacts.

Obama and his European counterparts have called on Putin to de-escalate. The Russian leader says he’s defending Ukraine’s ethnic Russians, who make up 59 percent of Crimea’s population.

U.S. Secretary of State John Kerry said March 6 in Rome that he presented Russian Foreign Minister Sergei Lavrov with ideas to take to Putin, and a State Department official said Kerry then debriefed Ukrainian Prime Minister Arseniy Yatsenyuk on his talks with Lavrov. Russia’s Interfax news service reported yesterday that Kerry and Lavrov, who met this week at other events in Paris and Rome, will continue their talks soon.

Sanctions Talk

Chinese Foreign Minister Wang Yi said today at a briefing that the priority was to exercise restraint in Ukraine. The situation should be handled in a prudent way, he said.

The U.S. and European allies will move together to impose sanctions if there isn’t a quick resolution Obama said at the White House on March 6. He telephoned German Chancellor Angela Merkel yesterday to discuss Ukraine, the White House said.

In a phone conversation, Lavrov warned Kerry against “hasty and ill-considered moves that can damage Russian- American relations, especially sanctions, which would inevitably boomerang on the United States,” the Russian Foreign Ministry said in a statement cited by Interfax.

Russian Defense Ministry is considering suspending visits of international inspectors as part of strategic arms reductions treaty obligations, Interfax reported today, citing an unidentified high-ranking military diplomat.

Gas Threat

Any sanctions the EU imposes would be done progressively as the 28-nation bloc seeks a diplomatic solution with Russia, EU Trade Commissioner Karel De Gucht said during a visit to the U.S. “The longer it takes, the broader the sanctions will be,” he said in a phone interview, without providing details.

Russia also turned up the economic pressure on the Kiev government by signaling that natural gas supplies may be cut because Ukraine’s unpaid gas bills have reached $1.9 billion. OAO Gazprom halted supplies to Ukraine five years ago amid a pricing and debt dispute, curbing flows to Europe.

Hungary, Poland, Slovakia and the Czech Republic are urging the U.S. to boost gas exports as a hedge against a Russian gas cut-off, the Associated Press reported today, citing a letter sent yesterday to House Speaker John Boehner.

Eni SpA Chief Executive Officer Paolo Scaroni said he doesn’t think the Ukraine crisis will affect gas supplies this year, thanks partly to mild weather in Europe, according to an interview with Italian daily La Stampa.

EU Aid

To steady Ukraine’s finances, the EU plans to provide an 11 billion-euro ($15.3 billion) aid package and is prepared to drop tariffs on about 85 percent of the bloc’s imports of Ukrainian goods, according to De Gucht.

The Republican-led U.S. House of Representatives passed a bill on March 6 to allow $1 billion in loan guarantees for Ukraine sought by Obama’s administration. Senate Foreign Relations Committee Chairman Bob Menendez, a New Jersey Democrat, is working with committee Republicans on a package of aid for Ukraine and sanctions against Russia. The panel is scheduled to vote on the legislation, which hasn’t yet been made public, on March 11.

Ukraine wants as much as $15 billion from the International Monetary Fund, which sent a mission to Kiev this week.