Russia ? A bomb detonated by remote control killed at least three police officers on patrol in Dagestan on Saturday, the latest violence to hit the troubled Russian region amid continuing fears about spreading violence in the Caucasus.

The bomb exploded Saturday afternoon as a four-man patrol walked past a grove of trees along a downtown street in Makhachkala, the capital of the Caspian Sea region, said city police Lt. Col. Akhmed Magomedov.

An Associated Press reporter saw two dead bodies with police uniforms lying on the street as armed police, firefighters and paramedics rushed to the scene. Dazed residents watched as workers swept broken glass from the street.

Two officers died at the scene, and one died en route to the hospital, officials said. A fourth officer was hospitalized in serious condition.

“I was walking by the fence, and suddenly I heard the explosion. I ran up and saw four police men on the ground. Two of them were dead,” Timur Aliyev said.

NTV showed footage of a partially collapsed blue fence and a blue van with its windows blown out.

There was no immediate claim of responsibility for the blast.