"The Prosecutor General's office is seeking to have the verdict overturned for being illegal and unsubstantiated," the source said.
Prosecutors in the case claimed Kazbek Dukuzov and Musa Vakhayev had gunned down Klebnikov on July 9, 2004, on the orders of Chechen businessman Khozh-Akhmed Nukhayev. He allegedly wanted revenge after Klebnikov wrote a critical book, "Conversations with a Barbarian", with him as the central figure.
Dukuzov and Vakhayev were acquitted by majority jury verdict May 5 at the Moscow City Court, along with Moscow notary Fail Sadretdinov, who had also been charged in the Klebnikov murder case.
Sadretinov has since been rearrested on suspicion of fraud.
Prosecutor Dmitry Shokhin said earlier this month the acquittal would be appealed in the Supreme Court in the near future.
Klebnikov, a United States national, had worked for Forbes since 1989 and gained his reputation for investigating murky post-Soviet business dealings and corruption.
