VIENNA (Reuters) - An Austrian army colonel suspected of spying for Russia for 26 years was arrested on Friday after a court reversed a decision that there was no need to detain him pending trial.

The case is embarrassing for Austria, which has some of the closest relations with Russia in the European Union. Moscow denies any involvement in the case, which was made public this month and was uncovered after a tip-off from Britain.

“He has already been arrested,” the prosecutors’ office in Salzburg, where the recently retired colonel lives, said in a statement.

A court in Salzburg initially dismissed the prosecutors’ arguments that he posed a flight risk and might re-offend if he was not remanded in custody. After his release they appealed to a separate court, which on Friday ordered his arrest.

The details of the ruling were, however, being kept confidential due to the sensitivity of the investigation, the statement added. The colonel, whom they did not name, remains under investigation.

Austria chose not to join the majority of EU states that expelled Russian diplomats over the poisoning of former spy Sergei Skripal and his daughter in Britain. Moscow had denied British accusations of involvement in the nerve-agent attack.