* Ukrainian industrialist was detained on U.S. request
* U.S. authorities have investigated him since 2006
* Firtash is one of Ukraine's richest men (Adds Firtash comment, detail)
By Angelika Gruber
VIENNA, March 21 (Reuters) - Ukrainian industrialist Dmytro Firtash, wanted by the United States, was released from detention in Austria on Friday after posting bail of 125 million euros ($174 million), a Vienna court said.
One of Ukraine's most influential oligarchs, Firtash, 48, was arrested in Vienna on March 12 at the request of U.S. authorities, which have been investigating him since 2006.
U.S. prosecutors said last week the U.S. government would seek Firtash's extradition to face charges filed in a Chicago court arising from an investigation into international corruption. Firtash's Group DF company has called the case a "misunderstanding" that should be resolved soon.
The detention of Firtash, whose business concerns in gas trading and chemicals thrived under Ukraine's ousted president Viktor Yanukovich, has coincided with a sharp escalation in the country's political crisis that pits the West against Russia.
Firtash has said his detention is unfair and "without foundation" and he has accused Washington of acting for "purely political reasons", though U.S. and Austrian authorities have denied any link to the current Ukraine crisis.
He is not believed to be among Ukrainians and Russians targeted in sanctions lists drawn up by Washington and the European Union in retaliation for Russia's annexation of Crimea.
A Reuters photographer outside the detention centre where Firtash has been held said a black Mercedes car with tinted windows was seen leaving the building.
"The last week has been a testing time for my family and me. I would like to thank personally all my friends and colleagues who have supported me in this difficult period," Firtash said in a statement released through a Vienna public relations firm.
The firm said "the bail conditions prevent Mr Firtash from leaving the country". The bail money is a record sum in Austria.
Austria's Federal Crime Agency said last week Firtash was suspected of violating laws on bribery and of forming a criminal organisation in the course of foreign business deals.
A final decision on his extradition to the United States could take weeks. He has sworn not to leave Austria if he posted the record-high bail, which the court said took into account his wealth and the gravity of the allegations against him.
Firtash, who has hired the law firm of former Austrian justice minister Dieter Boehmdorfer to represent him, had appealed against the court order that he be kept in detention.
The industrialist could also appeal against the court's final extradition ruling and he could take the case to Austria's justice ministry if an appellate court were to rule against him.
Forbes Ukraine magazine last year put Firtash in 14th place on its Ukrainian rich list, setting his fortune at $673 million. (Additional reporting by Fredrik Dahl, Derek Brook and Leo Foeger; Editing by Gareth Jones)