President Vladimir Putin said Friday that Western investors arrested in Russia were innocent until proven guilty, and added that security services might be interfering too much in business matters.

His remarks follow the arrest of prominent US investor Michael Calvey and several colleagues in February, a case that has caused deep concern among foreign investors.

“As long as there is no guilty verdict, everyone is considered innocent, including Mr. Calvey,” Putin told a Russian economic forum.

The detention of Calvey, the head of the Baring Vostok fund, has cast a shadow over the Saint Petersburg International Economic Forum, Russia’s top annual business event.

He is being held under house arrest and claims the case stems from a shareholder dispute.

Putin has insisted the case is a matter for the courts to decide, but during the plenary session he criticised security services for their “unreasonable and sometimes simply illegal interference in the work of businesses.”

Calvey — a longtime advocate of investment in Russia — said Friday that he regretted not being able to attend the forum, as he had regularly in the past.

In a statement released by his lawyers, Calvey “expressed regret that it will apparently not be possible for him to attend SPIEF for reasons that are beyond his control.”

Calvey thanked the business community “for its remarkable solidarity and support” and expressed concern for four colleagues still in detention.