The two suspects, Ilya Pyanzin and Adam Osmayev, were apprehended in the wake of a Jan. 4 apartment explosion in Odessa that killed a third suspect.
An unnamed source close to the investigation told Kommersant that existing evidence does not offer definitive proof that the suspects arrested in the case were planning an assassination.
This evidence includes materials for building explosives, a laptop with videos and photographs, and statements from the suspects.
The source said information not released by the Ukrainian Security Service indicates only that the suspects were learning to make explosives and do not prove that any sort of terror act was being planned.
The videos and photographs show reconnaissance on the prime minister's movements, pictures of several large buildings in Odessa, and video of an unsuccessful attempt by the suspects to destroy a pipe using explosives, the source said.
Spokesman for the Odessa branch of the security service Igor Skurtov was unable to comment on evidence in the case, but said there have been no significant developments in recent days, the Kommersant report said.
Pyanzin, who was injured in the explosion, was arrested and initially charged with illegal handling of weapons and explosives, after components for building explosive devices were found in the burnt-out apartment.
Osmayev was arrested Jan. 27, and in a taped confession aired on state-controlled Channel One he detailed a plot to kill Putin.
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