The Kremlin on Tuesday brushed off allegations that Russian opposition leader Alexei Navalny was the victim of an intentional poisoning orchestrated by authorities, The Associated Press reported.

The Kremlin added there were no grounds for a criminal investigation so far since it hasn't been fully established what caused the politician to fall into a coma.

The Russian government's insistence that Navalny wasn't necessarily the victim of a deliberate poisoning came a day after doctors at a German hospital where the 44-year-old is being treated said tests indicated he was poisoned.

Moscow's dismissals elicited outrage from Navalny's allies, who claim the Kremlin was behind the illness of its most prominent critic.

Kremlin spokesman Dmitry Peskov said the accusations against the government “absolutely cannot be true and are rather an empty noise.”

“We do not intend to take it seriously," he added.

Peskov insisted he saw no grounds for launching a criminal investigation at this stage, saying that Navalny's condition could have been triggered by a variety of causes and determining what it was should come first.

“If a substance (that caused the condition) is found, and if it is determined that it is poisoning, then there will be a reason for an investigation,” Peskov said, according to AP.

Navalny, a politician and corruption investigator who is one of the fiercest critics of President Vladimir Putin, fell ill on a flight back to Moscow from Siberia on Thursday and was taken to a hospital in the Siberian city of Omsk after the plane made an emergency landing.

Over the weekend, he was transferred to the Charité hospital in Berlin, where doctors on Monday said they have found indications of “cholinesterase inhibitors” in his system.

These act by blocking the breakdown of a key chemical in the body, acetycholine, that transmits signals between nerve cells. Navalny is being treated with the antidote atropine.

Meanwhile, US Secretary of State Mike Pompeo said on Tuesday that if reports about Navalny’s poisoning “prove accurate, the United States supports the (European Union’s) call for a comprehensive investigation and stands ready to assist in that effort.”