The United States and several European governments have demanded the release of opposition leader Alexei Navalny from Russian detention.
Mr Navalny, 44, was detained soon after his flight from Germany landed in Moscow on Sunday.
He was returning to the country five months after he was almost killed in a nerve agent attack he blamed on the Kremlin. Moscow has denied involvement.
Russia's foreign minister dismissed condemnation of the arrest.
Sergei Lavrov said Western politicians were using the case to "divert attention" from domestic problems.


Russia's prison service said the Kremlin critic had violated the terms of his suspended sentence for embezzlement, and that he would remain in custody until a court ruling.
A court hearing was organised on Monday at a police station on the outskirts of Moscow. In a video released by his spokeswoman, Mr Navalny described the hearing as "lawlessness of the highest grade".
The US and European Union led calls for Mr Navalny to be freed, but stopped short of threatening any punitive action.
US Secretary of State Mike Pompeo said Russian authorities were trying to silence their critics, while incoming national security adviser Jake Sullivan said the Kremlin's "attacks on Mr Navalny are not just a violation of human rights, but an affront to the Russian people who want their voices heard".
France, Italy, Germany and the president of the European Commission were also among those calling for his release.
UK Foreign Secretary Dominic Raab described Mr Navalny's arrest as "appalling".
"Rather than persecuting Mr Navalny, Russia should explain how a chemical weapon came to be used on Russian soil," he said.
When Mr Navalny was poisoned last August, he was flown to Germany for emergency medical treatment. As he recovered, he said he intended to return to Russia. On Sunday, he made good on that pledge, boarding a flight despite warnings he would face arrest on landing.
The plane was packed with journalists, including from the BBC's Russian Service. Shortly before landing, the pilot announced that for "technical reasons", the plane was being diverted from Vnukovo airport, where thousands of Navalny supporters had gathered, to Sheremetyevo airport, causing a stir among the passengers.
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