Yulia Navalnaya, wife of Russian opposition leader and President Vladimir Putin critic Alexei Navalny, arrives at the Charite Mitte Hospital Complex, in Berlin, Germany, Aug. 25, 2020.
The central building of Charite hospital where Russian dissident Alexei Navalny is treating, seen behind the Chancellery in Berlin, Aug. 25, 2020.

The U.S. government said Tuesday it is “deeply concerned” about medical tests that indicate poisoning in the case of Russian opposition leader Alexei Navalny, currently hospitalized in Germany following a medical evacuation.

“If the reports prove accurate, the United States supports the EU’s call for a comprehensive investigation and stands ready to assist in that effort,” Secretary of State Mike Pompeo said in a statement, referencing the European Union.

The Russian government has dismissed accusations that it was involved in an attack on Navalny, who remains in an induced coma in Germany’s Charité hospital after becoming sick Thursday while on a flight to Moscow from Siberia. The airline on which the Kremlin critic traveled said it did not serve him food or drink. Navalny was videotaped drinking a cup of tea in an airport café while awaiting his flight to Moscow.

Allies of Navalny contend the Kremlin is responsible for his illness, and some are calling for an investigation into whether President Vladimir Putin was involved.
 
“These accusations absolutely cannot be true and are rather an empty noise,” Kremlin spokesman Dmitry Peskov told reporters Tuesday in Moscow.

An ambulance which is believed to transport Alexei Navalny arrives at the Charite hospital in Berlin, Germany, Aug.22, 2020.

Navalny was transferred last Saturday to the Charité hospital, where doctors said Monday the tests revealed signs of “cholinesterase inhibitors” in his system.
 
Cholinesterase is an enzyme that is critical for the normal function of the nervous system in humans, other vertebrates, and in insects. Inhibitors block a chemical, acetylcholine, that transmit signals between nerve cells.

Cholinesterase inhibitors are compounds used to alleviate symptoms of dementia, but they also have been found in chemical weapons and pesticides used to kill bugs.  

Peskov said there is no evidence to warrant an investigation into Navalny’s illness and suggested there could have been various causes.  

“If a substance is found, and if it is determined that it is poisoning, then there will be a reason for an investigation,” Peskov said.

FILE - Russian opposition activist Alexei Navalny (L) and his spokeswoman Kira Yarmysh (C) walk in Kostroma, Russia.

Navalny’s spokeswoman, Kira Yarmysh, tweeted Tuesday it is not surprising the Russian government is not willing to launch a probe at this time.

“It was obvious that the crime would not be properly investigated, and a culprit found. However, we all know perfectly well who that is,” Yarmysh wrote.

Experts have said it is premature to conclude how the agent may have entered Navalny’s system. Some experts have noted that Novichok, the Soviet-era nerve agent used to poison former Russian spy Sergei Skripal and his daughter in Britain more than two years ago, was a cholinesterase inhibitor.

Navalny is a politician and corruption investigator who is one of Putin’s harshest critics. German Chancellor Angela Merkel and other European officials have requested that Russia conduct a full investigation.

U.S. Deputy Secretary of State Stephen Biegun was expected to raise the issue during a visit to Russia that began Tuesday.