* U.N. special envoy escorted to airport
* Angry crowd had trapped him in cafe
* Crimea controlled by Russian forces (Adds details from U.N. officials, paragraphs 4-6)
SIMFEROPOL, Ukraine, March 5 (Reuters) - A U.N. special envoy was forced to abandon a mission to Ukraine's Russian-occupied Crimea region on Wednesday after being detained and besieged inside a cafe by a hostile crowd shouting "Russia! Russia!"
Dutch diplomat Robert Serry flew to Istanbul after the incident and, according to the United Nations, would head from there back to Kiev. His interpreter, Vadim Kastelli, said Serry was escorted to the airport without being given a chance to pick up his bags from his hotel and placed on the first flight out.
Kastelli, who was with Serry at the time, said the incident began when Serry was blocked by a group of men in civilian clothes after a meeting at a Ukrainian military compound. Kastelli said he saw no weapons, although a journalist for Britain's ITN television said Serry told him at least one of the men was armed.
According to U.N. Deputy Secretary-General Jan Eliasson, who spoke to reporters in New York by telephone from Kiev, Serry had been visiting the naval headquarters in the regional capital, Simferopol.
"On his way out, he was threatened and brought to his car. There were unidentified people, some of them armed, telling him to leave and go to the airport," Eliasson said. "He refused but his car couldn't move, and he decided he would depart (on foot)."
Eliasson said Serry felt "seriously threatened," though he dismissed as false earlier reports that Serry had been kidnapped.
Kastelli said the men insisted they should take Serry straight to the airport and out of the country, but Serry refused and eventually left his surrounded vehicle on foot. Kastelli said he became separated from Serry when the envoy left the scene.
The ITN journalist, James Mates, said Serry, currently the U.N. Middle East envoy and previously Dutch ambassador to Ukraine, later took shelter in a cafe and agreed to leave Crimea to end the standoff.
A Reuters photographer saw him being escorted by police through a crowd of about 100 angry demonstrators, some waving Russian flags.
Crimea is under control of Russian forces who seized it last week, although Moscow says "self-defence" units of men in uniform without insignia are not under its command.
Kastelli said Serry had intended to stay the night and had more meetings scheduled with regional officials the next day.
"The authorities in Crimea not only knew he was here, but it was a coordinated programme. I think that is why he decided to come without security," Kastelli said.
At the airport in Simferopol, Nikolai Rudkovsky, a Ukrainian member of parliament, said Serry had boarded a flight for Istanbul. Rudkovsky said: "He asked to me to tell you that his recommendation was that all sides sit down and look for an understanding."
Kastelli said he had spoken to Serry from the airplane.
"Robert said all the things that are happening show how concerned he is and concerned all the people of the world should be about what is happening in Crimea," he said. (Reporting by Vasily Fedosenko and Alissa de Carbonel in Simferopol; Additonal reporting, Peter Graff in Kiev and Louis Charbonneau in New York; Writing by Peter Graff; Editing by Timothy Heritage and Jonathan Oatis)