MAKHACHKALA, March 20 (RIA Novosti) - A helicopter gunner has died and three police officers and one serviceman have been injured during an anti-militant operation in the Russian republic of Daghestan, a police spokesman said on Friday.

The ongoing operation started on Wednesday in Daghestan's Karabudakhkentsky District, some 30 kilometers to the south of the republic's capital of Makhachkala.

After a battle between police and gunmen on Thursday afternoon, officers discovered a group of up to 15 militants hiding out in a local forest. The group is led by Magomedali Vagabov, who is on a federal and international wanted list for crimes including attacks on Russian police. Vagobov's father and brother were earlier killed in clashes with the Russian security forces.

"The special operation did not end at night. Militants several times tried to break through, but were forced back by gunfire," the spokesman said.

Three officers suffered minor injuries and one was hospitalized with a head wound. The helicopter gunner, who was injured on Thursday afternoon, died in hospital during the night.

Fighting continued in the region on Friday morning, with helicopters circling the forest and sporadically opening fire. The militants have been completely surrounded, and additional forces, including Vympel special purpose troops, have been brought in.

The incident is the latest in series of clashes between militants and federal forces in the mountainous republic.