(CNN) Special counsel Robert Mueller's office appears to be in an early stalemate in its efforts to bring a criminal case against Russians allegedly involved in Moscow's efforts to influence the 2016 presidential election.

Although one Russian company indicted by Mueller in February, Concord Management and Consulting, has US attorneys and a court hearing scheduled, the special counsel's team hasn't been able to reach the company or its co-defendants.

The Russian government's top legal office wouldn't accept paperwork from US law enforcement in the case, and the company has already hit back at Mueller by demanding more evidence and information.

The tit-for-tat was revealed in a court filing Friday when Mueller's prosecutors asked to reschedule a hearing about the criminal case against 13 Russians and associated companies, who allegedly influenced the election using social media. The hearing was set for May 9.

The situation shows how difficult it will be for Mueller to bring Russians to justice for allegedly interfering in the 2016 election.

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