Russia's Foreign Minister Sergei Lavrov said that German accusations over the case of Kremlin critic Alexei Navalny were "groundless".
Germany says Mr Navalny, who is being treated in a Berlin hospital, was poisoned in Siberia with a rare nerve agent, something Moscow disputes.
Russian police say they will ask Germany to allow their officers to question the opposition leader.
The 44-year-old Kremlin critic and anti-corruption campaigner became ill after boarding a plane in Siberia and was admitted to hospital there before being flown to Berlin.
Germany claims there is "unequivocal evidence" that he was poisoned with a Novichok nerve agent but Russia says its doctors found no trace of any poison.
The Siberian transport police, who have been retracing Mr Navalny's movements, said in a statement that Russia would be preparing a request for its officers and an "expert" to shadow German investigators.
The police said following reports that Navalny had emerged from a coma, officers could "ask clarifying and additional questions" and be present as "German colleagues carry out investigative activities with Navalny, medics and experts".
The case has prompted international calls for Russia to carry out a transparent investigation or risk sanctions, but the country has not opened a criminal investigation because it says its medics did not find evidence of poison in tests.
Siberian transport police have been conducting a "check" into what happened and have published some findings on Mr Navalny's activities.
They said they had identified where Mr Navalny stayed and ate and that he drank "wine and an alcoholic cocktail". They confirmed that he visited the "Vienna Coffeehouse" at the airport of the city of Tomsk where supporters suspect he was poisoned with a cup of tea.
The police also said they had questioned all those accompanying Mr Navalny except for one woman, Marina Pevchikh, who "lives permanently in Britain".
They were now working to trace passengers on the flight from Tomsk to Moscow where Mr Navalny fell ill on 20 August, the statement said.
Russia has repeatedly complained that Germany has not answered its request to see the medical data that led it to declare that Mr Navalny was poisoned with Novichok nerve agent.
Russian doctors nevertheless said they administered an antidote to nerve agents that was also used by doctors at the Berlin hospital now treating the anti-corruption campaigner.
