KIEV, Ukraine -- Russia's President Vladimir Putin was showing no signs Saturday of heeding Western calls to ease the standoff in Crimea, where pro-Kremlin forces stepped up their takeover of the Ukrainian region preparing for a separatist referendum.
Gunmen fired warning shots as international observers tried to enter Crimea for a third day, and a Ukrainian border patrol plane came under fire that didn't cause injuries. TV5 reported that a military agency in the regional capital Simferopol was captured and 70 unidentified trucks entered the city.
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, threatens to 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.
Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry discussed the situation by phone Saturday, agreeing that "intensive contacts" were necessary to resolve the crisis, according to a statement by the Foreign Ministry in Moscow. Mr. Kerry said Thursday in Rome that he had presented Mr. Lavrov with ideas to take to Mr. Putin.
As Mr. Putin opened the 2014 Paralympic Games in Sochi on Friday, lawmakers in Moscow pledged to accept the results of a March 16 referendum on Crimea joining Russia.
The peninsula, where Russian speakers compose a majority, will join Russia once Parliament in Moscow passes the necessary legislation, and there's nothing the West can do to stop the process, according to Sergei Tsekov, the deputy speaker of Crimea's parliament.
"There's no comeback, and the U.S. or Europe can't impede us," Mr. Tsekov said by phone Friday from Moscow, where he met Russian officials to discuss the region's future. "Crimea won't be part of Ukraine anymore. There are no more options."
President Barack Obama had a phone conversation Saturday with French counterpart Francois Hollande and agreed that there's no legal basis for the referendum and that Russia should withdraw its forces, according to an emailed statement from Mr. Hollande's office.
Mr. Obama and Mr. Hollande are seeking direct dialog between Ukraine and Russia as well as the restoration of Ukraine's sovereignty and territorial integrity, according to the statement.
Russian Deputy Foreign Minister Grigory Karasin met Saturday with Volodymyr Yelchenko, Ukraine's ambassador to Moscow. The two discussed the countries' relations in a "frank atmosphere," the Russian Foreign Ministry said in a statement on its website.
Germany wants to "mobilize an as-broad-as-possible international coalition" to counter Russian threats over Ukraine, Frankfurter Allgemeine Sonntagszeitung reported, citing unidentified people from the Foreign Ministry.
A Ukrainian division at Shcholkino was stormed by Russian soldiers, who beat servicemen, confiscated their mobile phones and forced them and their families to leave, Ukraine's border guard service said in a statement. 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. Armed men attacked and entered a Ukrainian base in Sevastopol, the Defense Ministry in Kiev said Friday. The men withdrew after talks, according to TV5.
Gunmen on Saturday blocked observers from the Organization for Security and Cooperation in Europe from entering Crimea to monitor events there for a third day, Tatyana Baeva, a spokeswoman for the 57-state organization that includes Russia and the U.S., said by phone from Vienna. Nobody was injured as warning shots were fired, she said. Russia isn't taking part in the mission.
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.