As the standoff between Russian and Ukrainian warships and troops hardened Wednesday, foreign military observers were on their way here to monitor movements of self-defense militias and Russian ­forces.

A U.N. envoy was forced to abandon a separate fact-finding mission after encounters with pro-Russia militiamen and an angry crowd.

Pro-Russian forces also have blockaded Ukrainian military bases that haven’t surrendered in the Crimea region, says Sergei Aksyonov, the new leader of Ukraine’s Crimea region, the Associated Press reports.

Aksyonov also told the AP that the pro-Russian forces control all access to the peninsula.

The Organization for Security and Cooperation in Europe, an intergovernmental group devoted to crisis management, said 18 of its participating states were sending 35 observers to Ukraine “to dispel concerns about unusual military activities.” The United States is one of the parties.

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Ukraine’s National Security and Defense Council secretary, Andriy Parubiy, accused Russia of redeploying its troops in Crimea to hide its actions from the OSCE mission. “It's obvious that the so-called self-defense units were only a cover. The most active actions were carried out by special ­forces and Russian servicemen,” he said at a briefing Wednesday, according to the Interfax news agency.

Crimea continued to simmer, a day after Russian President Vladimir Putin insisted that troops in the region were well-trained Crimean self-defense units, and not members of his military.

In Simferopol, the regional capital, U.N. special envoy Robert H. Serry was accosted by unidentified armed men after he visited a naval headquarters in the city, U.N. Deputy Secretary General Jan Eliasson told reporters by phone from Kiev, Ukraine’s capital.

Eliasson said the group of 10 to 15 men blocked the Dutch diplomat’s car and ordered him to go to the airport and leave Crimea immediately.

“He refused” and left the vehicle to walk back to his hotel, Eliasson said, adding that Serry told him by phone that he is “in good shape physically.”

In the Sevastopol harbor, three Ukrainian navy ships remained boxed in by warships and tugboats from Russia’s Black Sea Fleet, whose commanders have called on the navy ships’ officers to pledge their allegiance to the new pro-Russia authorities in Crimea. They have refused.

“It’s a terrible situation. Everyone is very tense,” said Natasha Pechenik, wife of one of the officers aboard the navy command ship U510 Slavutych.

Standing on a hill, looking down at the ship, Pechenik and her friends confronted a group of armed men in military uniforms standing nearby. The men described themselves as self-defense units.

“Who are they kidding? Russians are our neighbors. We know Russian accents. I’m from a Russian family. These are Russians,” said Sergiy Shirokov, a retired Ukrainian coast guard officer.

Pechenik said she had earlier asked the soldiers, “Who are you defending us from? You’re the ones with guns.”

Crimea’s newly appointed pro-Russian regional prime minister, whose legitimacy has been questioned because he was installed after masked gunmen seized the Crimean parliament, said his administration was not speaking with the national government in Kiev.

“We don’t consider this government that proposes talks to us to be legitimate; that is the main issue,” Sergei Aksyonov told a Latvian radio station.

Russian officials continued to deny that their ­forces were spread out across the Crimean Peninsula. Russian Foreign Minister Sergei Lavrov, speaking in Madrid, said Wednesday that all the armed men who arrive in Russian troop transports, with Russian plates, are local self-defense militias.

In Moscow, Russian Defense Minister Sergei Shoigu denied Wednesday that any of his troops had strayed from their bases in Crimea despite videos and photos that suggested otherwise.

“No, absolutely not,” he responded when asked by Kremlin pool reporters whether there were any Russian troops in Crimea outside their own ­bases.

Videos show troops in Crimea saying they are Russian, despite wearing uniforms without any insignia. But Shoigu echoed Putin’s statements that the men were Crimean. “Of course, these are provocations,” he said, regarding the videos. When asked how Crimean self-defense troops could have come into possession of Russian Tiger and Lynx armored vehicles, he said he had no idea, the Interfax news agency reported.

On Tuesday, Secretary of State John F. Kerry almost mocked Russian denials that its troops were surrounding Ukrainian military ­bases. “The contrast really could not be clearer: determined Ukrainians demonstrating strength through unity, and the Russian government out of ex­cuses, hiding its hand behind false­hoods, intimidation and provocations,” he said in a visit to Kiev.

French Foreign Minister Laurent Fabius said Wednesday, “We cannot accept, we members of the international community, a country that invades another.”

Lally reported from Moscow. Anne Gearan in Paris and Carol Morello in Sevastopol contributed to this report.