(Adds fourth explosive device in paras 4, 5, background in last para)

MAKHACHKALA, March 10 (RIA Novosti) - Two bombs have gone off in the capital of the southern Russian republic of Daghestan, police said on Tuesday, adding that no injuries had been reported.

The bombs exploded at around 11:30 p.m. (20:30 GMT) on Monday in downtown Makhachkala. The blasts took place near a residential building and had a combined force of the equivalent of 8 kg of TNT.

Bomb disposal experts later discovered and defused a third bomb, equivalent to 2 kg of TNT.

On Tuesday, another explosive device was found on the outskirts of Makhachkala.

"An unidentified explosive device was found on the outskirts of Makhachkala," a police official said. "Bomb disposal experts are working at the scene. Experts with sniffer dogs have confirmed the plastic bag with wires coming out of it contains explosives."

In a separate incident on Monday, gunmen opened fire on a police station in Daghestan's Buynaksk District. No police officers were injured in the attack, police said.

Daghestan and Ingushetia have seen a rise in violence recently linked both to militants based in neighboring Chechnya and local criminal groups. Attacks on officials, police and troops are common in Russia's North Caucasus.