Russia conducted an “anti-terrorist operation” in the southern region of Dagestan on Sunday, arresting three people, the National Anti-Terrorism Committee said.

Russia has been on high alert since the attack on the Moscow concert hall on March 22, the deadliest attack in the country in 20 years with at least 144 dead.

“Security agencies arrested three robbers who were planning a series of terrorist crimes. During the inspection of the premises where the criminals were kept, automatic weapons, ammunition and an improvised explosive device were found ready for use,” the commission said on Sunday.

Earlier, the commission said that suspected criminals were blocked by security services in several apartments in residential areas of the regional capital Makhachkala and one of the republic’s largest cities – Kaspiysk.

There were no civilian casualties and no casualties among law enforcement personnel.

The “state of anti-terrorist operation” in both Makhachkala and Kaspiysk was lifted at 12:00 local time (09:00 GMT), according to Makhachkala Mayor Yusup Umavov.