Sept. 9 (UPI) -- The Group of Seven foreign ministers have denounced the "confirmed poisoning" of Russian opposition leader Alexei Navalny.
The foreign ministers in a statement Tuesday said they are united in condemning the poisoning of Navalny "in the strongest possible terms."
Navalny, a vocal critic of Russian President Vladimir Putin, is in serious condition at a Berlin hospital receiving treatment after falling ill on a flight from Tomsk, Russia, to Moscow late last month.
The plane was forced to make an emergency landing in Omsk before Navalny was moved to Germany, where doctors confirmed he had been poisoned.
The G7 foreign ministers said Germany briefed them on its findings that the Russian activist was "the victim of an attack with a chemical nerve agent."
Doctors determined the chemical used was of the Novichok group, a Soviet-era nerve agent that killed former spy Sergei Skripal and his adult daughter in 2018.
Russia has denied being behind Navalny's attack.
In the strongly worded statement, the foreign ministers rebuked the use of chemical weapons and told Russia to hold those responsible for poisoning Navalny accountable.
"We, the G7 foreign ministers, call on Russia to urgently and fully establish transparency on who is responsible for this abhorrent poisoning attack, and bearing in mind Russia's commitments under the Chemical Weapons Convention, to bring the perpetrators to justice," they said.
The foreign ministers described the attack as a blow to democracy and political plurality and called it a threat to those who fight for freedom in Russia.
"We will continue to monitor closely how Russia responds to international calls for an explanation of the hideous poisoning of Mr. Navalny," they said. "We remain strongly committed to our support for democracy, the rule of law and human rights in Russia and to bolster our support to the Russian civil society.
The foreign ministers of Canada, France, Germany Italy, Japan, Britain, the United States and the European Union endorsed the letter, which was issued by the U.S. State Department.
The human rights leader said the number of targeted assassinations or poisonings of current or former Russian citizens on domestic and foreign soil over the last two decades is "profoundly disturbing" and warrants a "thorough, transparent, independent investigation."
House Democrats also urged President Donald Trump on Tuesday to open a U.S. investigation into the poising of Navalny.
In a letter, Reps. Eliot Engel, D-NY, chairman of the House committee on foreign affairs, and Michael McCaul, R-Texas, a ranking member in the committee, said the investigation is required under U.S. law.
"If the Russian government is once again determined to have used a chemical weapon against one of its own nationals, additional sanctions should be imposed," the lawmakers wrote. "Those responsible for this despicable attack must be held accountable, and Russian President Vladimir Putin must know that he and his cronies will not be allowed to violate international law and impunity."
Last week after Germany confirmed that Navalny had been poisoned, Trump told reporters that he hadn't seen "proof" but would look into the incident.
"I don't know exactly what happened," he said from the White House on Friday. "I think it's tragic. It's terrible. It shouldn't happen. We haven't had any proof yet, but I will take a look."