When asked about the statement from Berlin's Charité hospital that said its tests indicated Navalny had been poisoned, Peskov said Russian and German doctors had the same findings, "but the conclusions differ".
"It was clear after his arrival that security measures had to be put in place because we are dealing with a patient who was likely the target of a poison attack", said German government spokesman Steffen Seibert, who added that other Kremlin critics have been poisoned in the past few years.
Dr. Thomas Hartung, of the Johns Hopkins Bloomberg School of Public Health in Maryland, said such substances are easy to detect, even days and weeks after the poisoning, and that "we will know soon which substance was used".
"The Russian leadership definitely doesn't", the Foreign Ministry said Tuesday.
U.S. Secretary of State Michael Pompeo joined Merkel's call for an inquiry, saying in a statement on Monday that the country was "deeply concerned" by the preliminary results of a poisoning.
Citing unrest directed at the Kremlin in Russia's Far East and a popular uprising against Belarus's Putin-backed leader, Alexander Lukashenko, Kortunov said the spiraling chaos could prompt the West to see the poisoning of a prominent opposition figure "as a sign that Putin is losing control of the situation".
Replying to a question on the possible worsening of relations between Moscow and the West, Peskov said: "Of course we would not like this (to happen), that's the first thing". His condition is serious, but there is no acute danger to his life, it added.
European Union trade chief says he complied with health rules on Irish trip
Trade is a central issue in the EU's efforts to build agreement with the United Kingdom to mitigate any ill-effects from Brexit. It emerged that the EU Commissioner attended the Oireachtas Golf Society dinner in Clifden last week.
While the exact poison hasn't been identified yet, the toxins found in Navalny's body belong to a group of chemicals - cholinesterase inhibitors - the same group that contains the Novichok nerve agent used in the attack on Russian dissident Sergei Skripal in the United Kingdom in 2018.
The pressure on Russia following Navalny's illness has hit Russian markets, with the rouble tumbling on Wednesday to four-year lows against the euro.
Cholinesterase inhibitors are a broad range of substances that are found in several drugs, but also in pesticides and nerve agents.
"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.
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 wife of Russian opposition leader Alexei Navalny, Julia, left, arrives at Berlin's Charite Hospital on August 25, 2020.
Merkel is calling on Russian officials to carry a full investigation of the poisoning of Navalny.