Rupert Murdoch’s London offices of 21st Century Fox’s Fox Networks Group were raided by European Commission investigators on Tuesday, The U.K.’s Daily Telegraph reported Tuesday.

Authorities were told to keep details of their probe confidential and investigators are expected to be on site through Wednesday and possibly Thursday, according to the Telegraph and other news outlets.

Fox News and 21st Century Fox did not immediately respond to TheWrap’s request for comment. But a spokesman for 21st Century Fox said in a statement Tuesday that Fox Networks Group is “cooperating fully” with the inspection.

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According to the Daily Telegraph and other outlets, among the objects seized were documents and computer records.

The probe comes as 21st Century Fox attempts a takeover of Sky, which has come under scrutiny by British regulators.

Earlier this year, the U.K.’s Competition and Markets Authority said it had concerns over the deal, which the agency said could put too much influence in the hands of the Murdoch family.

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Shares of Fox fell more than 1 percent in extended trading, according to CNBC.