The United Nations special envoy on Ukraine was forced to leave Crimea after being stopped by gunmen and surrounded by a crowd on Wednesday.
Robert Serry cut short his diplomatic efforts after a group of armed men harassed, followed, then trapped him in a coffee shop in Simferopol, he told reporters.
"This harassment and intimidation is unacceptable," said U.S. Ambassador to the UN Samanta Power, in an exclusive interview with VOA at the United Nations.
Crowds shouted pro-Russian slogans as Serry headed to the airport.
UN Deputy Secretary-General Jan Eliasson, on a mission in Kyiv, said Serry is in "good shape physically" and denied initial reports that he had been kidnapped.
"He felt physically threatened and he expects all authorities to have control of the situation," Eliasson said.
The men appeared to be part of the irregular, pro-Russian volunteer forces -- sometimes described as gangs -- whose numbers have increased since the appearance of unidentified soldiers in the Ukrainian region over the past week. Those troops are widely believed to be Russian.
Also Wednesday, anti-European protesters gathered at the hotel where representatives from Organization for Security and Cooperation in Europe.
One demonstrator, Simferopol resident Raisa Ivanovna, said she wants Crimea to remain part of Ukraine, but with more autonomy. She said she is against any OSCE interference in their affairs of state.
The Crimean peninsula has been a flashpoint of diplomatic contention, with Western leaders denouncing what they call Russian aggression here. Russia denies it has deployed troops beyond leased military bases, a statement not believed by even many pro-Russian Crimeans.