LONDON, (Reuters) – Alexei Navalny, a Kremlin critic who was jailed in Russia on Tuesday said he had been arrested in a new criminal investigation and could face up to 15 years more on top of the existing sentence if convicted.

Navalny stated that he had been accused of creating an extremist group and encouraging hatred toward the authorities in social media posts. This is on top of the nine year sentence that he already received for fraud and contempt in March. He was also serving a two-1/2 year sentence.

Navalny stated on Twitter that “not even eight days have passed” since the nine-year-long high-security sentence was in force. Today, Navalny formally charged him with a new case.

It turned out I had created an extremist group to inspire hatred against officials and oligarchs. After being put in prison, I called for protests and was mad at them. He said that they were supposed to increase my sentence by 15 years.

It was not immediately confirmed that the charges had been raised.

Western politicians as well as human rights organisations have condemned various criminal proceedings against Navalny. He is the most visible opponent of President Vladimir Putin in recent decades.

Multiple European medical facilities have concluded that Navalny, who was on campaign in Siberia at the time, was poisoned by nerve agents. He was released from hospital in Germany after receiving medical attention for months.

The Kremlin’s decades-long effort to suppress and silence Russia’s internal opposition has been intensified following the invasion of Ukraine. Navalny has taken a stand against the war. He attacked Putin at a court appearance, calling it “stupid” as well as “built on lies”.