Moscow (CNN) Michael Calvey, a US citizen and one of Russia's most prominent foreign investors, has been detained in Moscow in connection with a large-scale fraud investigation, a spokeswoman for a Moscow court told CNN on Friday.

Calvey is the founder of Baring Vostok Capital Partners, an investment company established in 1994 that has raised at least $3.7 billion in capital, according to its website.

A Russian court ordered Friday that Calvey's detention be extended for 72 hours, Moscow's Basmanny court spokeswoman Yunona Tsaryova told CNN.

When asked about the charges against Calvey, Tsaryova declined to comment but said that a session would take place Saturday to impose pretrial restrictions.

Russian state news agency RIA Novosti reported Calvey was detained along with five others, including three Baring Vostok employees; Alexey Kordichev, chairman of the board of directors of Vyatka Bank; and Maxim Vladimirov, general director of Perviy Collector Bureau, a debt collection company.

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