A senior police officer has been arrested, as well as being suspended on suspicion of gross misconduct.
Cleveland Police's assistant chief constable, Adrian Roberts, was released while investigations continued.
The force has not revealed what the allegations against him are.
A referral was sent to the Independent Office for Police Conduct which said the "alleged conduct matters" had taken place outside of England and Wales so they fall outside its jurisdiction.
Cleveland Police been rocked by a number of scandals in recent times and has had five chief constables in just six years.
Richard Lewis was last week unveiled as the replacement for Mike Veale who quit in January.
Mr Veale was facing an IOPC investigation following "serious" allegations about his behaviour.
A Cleveland Police spokesman confirmed the suspension of a "senior officer", adding: "There is a presumption of innocence throughout any investigative process which is right, fair and proper.
"Suspension is a neutral act and it is important for all those concerned and the integrity of the investigation that the individual concerned is innocent unless demonstrated otherwise.
"We can confirm that the officer concerned has been arrested and released under investigation."
Cleveland's Police and Crime Commissioner, Barry Coppinger, said he had received "a detailed briefing" on the matter and was assured the force had "taken the necessary steps in these circumstances".
A spokesperson for the Independent Office for Police Conduct said: "We received a referral from Cleveland Police on 10 April regarding the conduct of a senior officer.
"The referral has been returned to the force for their action because the alleged conduct matters are reported to have taken place outside of England and Wales so they fall outside of our jurisdiction.
"We have informed Cleveland Police of our decision and asked that if any conduct matters come to light that fall within our remit, they should refer them for our immediate consideration."