Kremlin critic Alexei Navalny, who fell gravely ill on Thursday after what his allies believe was a poisoning, was under intense police surveillance in preceding days, a Russian tabloid newspaper cited law enforcement sources as saying.

Police officers guard the hospital where Alexei Navalny is receiving medical treatment in Berlin

Berlin:

Before he collapsed on a flight during a trip to Siberia Navalny was followed by plainclothes FSB officers and his movements were closely monitored via CCTV, the report in the Moskovsky Komsomolets newspaper said.

Navalny, a long-time opponent of President Vladimir Putin and campaigner against corruption, was flown in an air ambulance on Saturday for treatment in Germany.

Navalny, 44, was in an induced coma when he was evacuated from the Siberian city of Omsk, but there has been no word yet from the Charite hospital in Berlin on his condition.

His team were due to host a briefing via YouTube on Sunday evening to discuss “everything we know so far about Alexei’s poisoning,” but subsequently cancelled it saying they were not ready, press secretary Kira Yarmysh and campaign HQ head Leonid Volkov wrote on Twitter.

Citing security service sources, the Moskovsky Komsomolets described the timeline of his trip before he fell ill down to the number of rooms his team booked in a local hotel and the fact that Navalny chose not to sleep in the room booked under his name.

An apartment rented for him by one of his supporters was discovered by police surveillance, the paper reported, when a sushi takeaway was ordered to the address by one of Navalny’s supporters.

“The scale of the surveillance does not surprise me at all, we were perfectly aware of it before,” Yarmysh wrote on Twitter.

“What is surprising, however, is that (security service sources) did not shy away from describing it.”

In its report, the Moskovsky Komsomolets paper cited security sources as saying that their surveillance of Navalny’s movements did not reveal any suspicious contacts that could be related to his illness.

Security services believe that if Navalny was poisoned, the incident took place either in the airport or on the plane, the newspaper wrote.

However the paper said they are still awaiting results of laboratory tests of samples taken by police from all the places Navalny and his team visited on their trip, including samples of the air.

Initial results are expected on Monday, with results from tests for radioactive material due later in the week, the paper said. It did not say whether or not these would be made public.

Doctors at the hospital in Omsk where Navalny was treated before his evacuation to Germany have said they do not believe he was poisoned. They diagnosed him with a metabolic disease that may have been caused by low blood sugar.

Kremlin spokesman Dmitry Peskov said on Friday that it was still unclear what caused Navalny to fall ill. He had previously said that any poisoning would need to be confirmed by laboratory tests and that doctors were doing everything they could to help Navalny.