Russian authorities say they have detained a Ukrainian member of a Crimean-Tatar activist group that has led a blockade of the annexed peninsula.

The Federal Security Service (FSB), Russia’s main security agency, said on February 17 that Seit-Ibragim Zaitullaev attempted to "illegally" cross into Crimea, which Moscow seized and annexed from Ukraine in 2014.

An FSB statement cited by Russian state news agencies claimed it found evidence that Zaitullaev belongs to a Crimean-Tatar organization called Asker, which has spearheaded a civilian-led blockade along the border with the Moscow-controlled peninsula.

There was no immediate comment from the Ukrainian government.

Lenur Islyamov, the leader of Asker, confirmed to RFE/RL Russian Service reporter Anton Naumlyuk that Zaitullaev was previously a member of the organization but said he had left the group two months ago.

Russia seized control of Crimea from Ukraine in March 2014 after sending in troops to secure key facilities and staging a referendum dismissed as illegitimate by Ukraine, the United States, and more than 100 countries in the United Nations General Assembly.

Russia has since made it a criminal offense to question Russia's territorial integrity within what the government claims are its borders.

Rights watchdogs and Western governments have accused Moscow of carrying out a broad crackdown on independent media and dissent in Crimea.

The FSB statement said Zaitullaev faces charges of "illegally crossing the border of the Russian Federation."

The statment claimed Zaitullaev told investigators that Asker "prepares specialists for acts of sabotage in Crimea," Russia’s state-run TASS news agency reported.

That language echoes allegations against at least five Ukrainian citizens arrested by Russian law-enforcement agencies in Crimea in November.

The FSB described them as suspected members of a Ukrainian "saboteur group."

Ukraine's Defense Ministry called those allegations "another fabrication of the Russian secret services aimed at justifying its own repressive measures against local residents and [discrediting] Ukraine [in] the international arena."

With reporting by RFE/RL’s Russian Service, the Crimean Desk of RFE/RL's Ukrainian Service, TASS, and RIA Novosti