Lavrov said Western reports about the case were filled with "questionable facts" and "information from questionable sources" and were aimed at blackening Russia's image.
Lavrov suggested such a "trend" in Western reporting on Russia was part of an effort to weaken Russia as a competitor.
Lavrov was speaking on the day that British detectives returned to London after carrying out inquiries in Moscow.
A Scotland Yard spokeswoman said the British detectives had been offered "satisfactory" cooperation from Russian officials.
The British detectives were not allowed to question witnesses themselves, but observed Russian prosecutors conduct the questioning.
(compiled from agency reports)