Russia announced that it has launched a police "check" into opposition leader Alexei Navalny's illness and has asked German medics treating him to share his medical records.
But the Kremlin continues to insist there are no grounds for a criminal investigation.
The German doctors have said tests on the 44-year-old politician and anti-corruption campaigner indicate that he was poisoned, and his allies have pointed the finger of blame at President Vladimir Putin.
In an interview on state-controlled television today, Mr Putin made no mention of the case.
Prosecutors said they had "no evidence" of a deliberate crime committed against Mr Navalny and requested that German medics hand over "the evidence for the initial diagnoses they gave" including test results.
He fell ill on a plane to Moscow from the Siberian city of Tomsk last Thursday and spent two days in a Russian clinic in a coma before being transferred to Berlin's Charite hospital.
Medics there said on Monday they do not know the exact substance involved but that Mr Navalny was apparently poisoned with a substance that inhibits the cholinesterase enzyme, a feature of nerve agents.
His allies say he may have been poisoned by a cup of tea he drank at Tomsk airport.
International calls have been mounting for an independent inquiry into the case, but Kremlin spokesman Dmitry Peskov dismissed the police check as routine, saying: "there is no basis for an investigation".
"Nothing has changed, we still don't have any understanding of what caused the state the sick man is now in," he told journalists.
Transport police in Siberia said they had started "a pre-investigation check" into what led to Mr Navalny's hospitalisation to establish "all the circumstances" and decide whether to open a criminal probe.
The police action appears to be a low-level response after his allies asked for an investigation into an attempted assassination of a public figure.
Police do such checks to determine whether a crime has been committed.
Mr Navalny's spokeswoman Kira Yarmysh tweeted that they had not been informed of the police check.
Prosecutors said that they began the check on the day he fell ill but did not say whether they plan to launch a criminal investigation.
Russian doctors said their tests did not find any trace of poison while they treated Mr Navalny with the same antidote, atropine, that German medics are using.
Police and plain clothed security service agents questioned doctors at the hospital without making any public statements.
Transport police said they searched locations that Mr Navalny visited and his hotel room, apparently referring to where he stayed in Tomsk.
They said they also examined security camera footage and confiscated "more than 100 items that could have value as evidence".
Police said that they did not find any "strong-acting or narcotic substances".
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Mr Peskov has repeatedly rejected international calls for a transparent investigation from Western leaders including British Prime Minister Boris Johnson and NATO chief Jens Stoltenberg.
French Foreign Minister Jean-Yves Le Drian said today he did not understand why Russia did not opt for transparency, which would be "to their credit."
Mr Peskov has argued it is not possible to say that Mr Navalny was poisoned since no toxic substance had been identified.
Mr Putin discussed the case with Italian Prime Minister Giuseppe Conte yesterday, the Kremlin said.
The Russian President rejected "rushed and groundless accusations" but said that Russia had an interest in a "scrupulous and objective investigation of all the circumstances."
Unusually, the Kremlin statement quoting him referred to Mr Navalny by name, while its practice has been never to do so.
The Russian foreign ministry said earlier this week that international statements alleging deliberate poisoning were "clearly not" in the Russian leadership's interests.