A federal jury in New York on March 7 found Vladimir Kuznetsov guilty of a single count of laundering more than $300,000.
Russian Foreign Ministry spokesman Mikhail Kamynin criticized what he called former UN Secretary-General Kofi Annan's "hasty" decision to strip Kuznetsov of his diplomatic immunity.
Kamynin also alleged that Kuznetsov and other witnesses were pressured by prosecutors in what he said were "gross violations of procedural rules."
Kuznetsov was arrested and charged in 2005 after an internal UN investigation.
He faces up to 20 years in prison. Sentencing is scheduled for June 25.