MOSCOW — A prominent hard-line nationalist who accused Russian President Vladimir Putin of weakness and indecision in Ukraine was arrested Friday on charges of extremism, a signal the Kremlin has toughened its approach with hawkish critics after last month’s abortive rebellion by the Wagner mercenary company.

Igor Strelkov, a retired security officer who led Moscow-backed separatists in eastern Ukraine in 2014 and also was implicated by the Netherlands in the downing of a Malaysia Airlines passenger jet that year, has argued that a total mobilization is needed for Russia to achieve victory. He recently criticized Putin as a “nonentity” and a “cowardly mediocrity.”

Igor Strelkov’s Criticism and Arrest

Moscow’s Meshchansky District Court ordered the 52-year-old Strelkov, whose real name is Igor Girkin, to be held in custody for two months pending a probe on charges of making calls for extremist activities. He faces up to five years in prison if convicted.

Strelkov rejected the charges, but asked the judge to place him under house arrest, citing health issues.

Aftermath of Wagner Mercenary Company’s Rebellion

Strelkov’s arrest comes nearly a month after a short-lived mutiny launched by mercenary chief Yevgeny Prigozhin that saw his Wagner troops capture military headquarters in the southern city of Rostov-on-Don and then drive as close as 200 kilometers (125 miles) to Moscow to demand the ouster of Russia’s top military leaders. Prigozhin agreed to end the June 23-24 rebellion under a deal that offered an amnesty to him and his mercenaries and allowed them to move to Belarus.

The revolt posed the most serious threat to Putin’s 23-year rule, eroding his authority and exposing government weakness.

Like Prigozhin, Strelkov harshly criticized Russia’s military leaders for incompetence, but he also denounced the Wagner’s chief and described his action as treason and a major threat to the Russian state. The two repeatedly had traded insults, and Strelkov’s supporters said a criminal inquiry into his statements has been initiated by one of Wagner’s mercenaries.

Strelkov has over 875,000 subscribers on his messaging app channel. The Club of Angry Patriots, a recently created hard-line group he belonged to, issued a statement protesting his detention as a “provocation” that “undermines the population’s trust in law enforcement organs” and “carries extremely negative consequences for the country’s stability.”

Strelkov served in the Russian military during the Chechen separatist wars and later joined the country’s top domestic security agency, the Federal Security Service, where he reached the rank of colonel.

After he retired from service, he took part in the Kremlin’s annexation of Ukraine’s Crimean Peninsula and then led fighters in eastern Ukraine during the first months of a Moscow-backed separatist rebellion there in 2014.