MOSCOW - Russia’s Foreign Minister Sergei Lavrov said on Friday that German accusations over the case of Kremlin critic Alexei Navalny were “groundless”.

Germany says Navalny, who is being treated in a Berlin hospital, was poisoned in Siberia with a rare nerve agent, something Moscow disputes.

Russian police have traced opposition politician Navalny’s movements and what he drank before falling ill in Siberia last month, and are trying to locate a witness who has left the country, the interior ministry said on Friday.

Russia has not opened a formal criminal investigation and is sticking to its position that it needs hard evidence from Germany that Navalny was indeed poisoned

The ministry said it was preparing another request for legal assistance from Germany, where Navalny was airlifted to hospital last month after what Berlin says was a poison attack on him with a Novichok nerve agent.

In a statement, the interior ministry’s transport department in Siberia said it wanted to send investigators to work alongside German colleagues on the case, after reports that Navalny had emerged from a coma.

“This request will include an application for the possible presence of Russian internal affairs investigators... and a Russian specialist when German colleagues are conducting investigations with Navalny, doctors and experts,” the ministry said in a statement.

It also requested permission to ask clarifying and additional questions.

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Russia has not opened a formal criminal investigation and is sticking to its position that it needs hard evidence from Germany that Navalny was indeed poisoned.

Transport police in Tomsk had established a timeline of events leading up to Navalny falling ill, the ministry said. It listed a hotel, restaurant, flat and coffee shop Navalny had visited, and said he had drunk wine and an alcoholic cocktail.

In the days following Navalny’s illness, his spokeswoman strongly denied allegations he had consumed alcohol.

READ MORE: Navalny taken out of coma, Berlin hospital says

The ministry said police had interviewed five of the six people it said accompanied Navalny on the journey when he fell ill. It said it was looking for a sixth person it named as Marina Pevchikh, a UK resident who flew to Germany on Aug. 22 and whose whereabouts it said were currently being established.