Russia on Tuesday issued an arrest warrant for Yulia Navalnaya, accusing the exiled opposition figure of participating in an "extremist organisation".
A court said it had "approved the request of the investigators and decided a preventive measure in the form of detention for two months".
Navalnaya has vowed to continue the work of her husband Alexei Navalny, Russian leader Vladimir Putin's main opponent who died in an Arctic prison in February.
Navalnaya slammed the warrant in a statement, saying :"Vladimir Putin is a killer and a war criminal. He belongs in prison".
The activist's team also dismissed the allegations.
Navalnaya "was arrested (in absentia!) for 'being a member of an extremist community' by the infamous Basmanny court of Moscow," wrote Leonid Volkov, Navalny's former chief of staff, on X.
"Quite a recognition of Yulia's determination to continue Alexei's fight!" he added.
German Chancellor Olaf Scholz on Tuesday also criticised Russia's move, calling the arrest order a "warrant against the desire for freedom and democracy" in a post on X.
Navalny's organisations have been outlawed in Russia, labelled an "extremist" group and put on an official "terrorist" list.
Navalnaya, an economist, stood by her husband as he galvanised mass protests in Russia, flying him out of the country when he was poisoned before defiantly returning to Moscow with him in 2021, knowing he would be jailed.
Following his death, Navalnaya vowed to take up her late husband's work and has lobbied against Putin's government from abroad.
During Russian elections in March, Navalnaya called for mass protests against Putin by forming long queues outside voting stations.
