Russian Caucasus extremists pledged allegiance to the so-called Islamic State forces this week in a recording posted online.

ISIS has welcomed the move by the militant group, which exists in four locations in Russia: Ingushetia, Chechnya, Dagestan and Kabardino-Balkaria regions. The YouTube voice recording was posted Sunday. In response, ISIS also posted another audio recording online.  

The Caucasus militant group swore obedience to ISIS mastermind, Abu Bakr al-Baghdadi. “Obeying the order of Allah, we are declaring our allegiance to Caliph Ibrahim ben Awwad ben Ibrahim al Badri al-Qoureishi al Husseini for obedience and subordination,” per AFP's story quoting the recording, “We testify that all mujahideen of the Caucasus are united in this decision, and there are no disagreements among us on this issue.”

ISIS spokesman Abu Mohammed al-Adnani welcomed the announcement in another recording Tuesday. The spokesman congratulated “the soldiers of Islamic State in the Caucasus.” The congratulatory message was in response to the Caucasus militants pledging allegiance to the Caliph. In the recording, Adnani declared that Baghdadi had named Sheikh Abu Mohammad al-Qadari as the governor of the Caucasus region.

Russian newspaper Pravda earlier reported that as many as 5,000 Russian citizens were fighting for ISIS forces. The CIS Anti-Terrorist Center head Andrei Novikov said that a part of the information had been “confirmed and documented.”

British Home Secretary Theresa May earlier advised radicalized nationals against traveling. She clarified that extremist groups like ISIS lured young women with “false promises of starting a new life,” the Guardian reported.

The Moscow Times reported that Varvara Karaulova, a 19-year-old philosophy student, had traveled to Turkey with a one-way ticket. Her father informed the Russian security services about her radicalized activities, and Turkish security and Interpol arrested her near Turkey’s border with Syria.

Russia Beyond the Headlines reported that Kristina Presnyakova, a 25-year-old Russian female who had joined ISIS forces, was included on the international wanted list. She traveled to Syria via Turkey in 2013 and received training at an ISIS camp.

A source said that a criminal inquiry had been opened against her. She is believed to be staying in the Syrian city of Al-Raqqah.