The ambassador's calls echoed the European Union's diplomatic chief Josep Borrell, who on Monday also called on Russian Federation to launch a "transparent" investigation into the apparent poisoning.
"Those responsible must be identified and held accountable, " Merkel said.
Cholinesterase inhibitors are found in nerve agents, pesticides and some medicines, including those that relieve symptoms of dementia.
The suggestion that Navalny was poisoned has been vehemently rejected in Russian Federation, where a number of Kremlin critics fell victims to suspected poisonings in recent years, since last week.
The cholinesterase inhibitors found in Navalny's system reportedly block the breakdown of acetycholine, a vital chemical that transmits signals between nerve cells.
This results in overstimulation of the junction between nerves and muscles. "This is why they are a favored method of poisoning people".
"The outcome of the disease remains uncertain, and long-term effects, especially in the area of the nervous system, can not be ruled out at this point in time", hospital officials said.
Navalny's wife, Yulia Navalnaya, has been visiting her husband daily and made no comment to reporters as she arrived Tuesday.
The plane made an emergency landing in the Siberian city of Omsk, where Navalny was hospitalized.
For the moment, he said, it's up to doctors in the clinic in Germany where Navalny was taken over the weekend after falling ill on a flight in Siberia to determine what the Kremlin critic was exposed to.
As of Monday, Russia's Investigative Committee had not opened a case, a spokeswoman for Navalny said.
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After 30 days, all of the United Nations sanctions previously placed on Iran would "snap back" into place. Ambassador Majid Takht Ravanchi speaks to reporters at U.N. headquarters in New York, Aug. 20, 2020.
"Now our words have been confirmed by tests in independent laboratories". However, we all know perfectly well who that is, ' Ms Yarmysh said.
The US ambassador in Moscow also called for an "immediate, comprehensive, and transparent investigation by the Russian authorities" today after the clinical findings emerged from Germany.
"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.
Peskov said he was puzzled by what he called German doctors' "hurry" to claim poisoning as the reason for Navalny's condition.
In the German capital, Charite doctors found a substance related to cholinesterase inhibitors.
Police vehicles outside Charite Hospital as Alexei Navalny undergoes treatment inside, in Berlin, on August 24.
Navalny's allies have blamed Russia's security services for poisoning him.
"I can't say who they were, " Murakhovsky said.
Like many other opposition politicians in Russia, Navalny has been detained by law enforcement and harassed by groups supporting Russia's government.
Last year, Navalny was rushed to a hospital from jail where he was serving a sentence on charges of violating protest regulations. Doctors said he had a severe allergic reaction and sent him back to detention the following day.