Dozens wounded as suicide bomber targets police in Southern Russia
A two-day special operation was launched on Friday in the city of Makhachkala against militants hiding out in one of the city's buildings.
The site was sealed off by security forces.
But on Friday night a suicide bomber attempted to break through the cordon.
Having failed, he blew himself up injuring at least 42 people.
Two Special Forces officers were also killed in gunfights.
Police found automatic weapons and a bomb-launcher in the house where the gunmen were cornered.
The region has been the target of escalating ethnic tensions and terrorism since the 1990s.
Earlier this month, three servicemen were killed and dozens injured in a suicide bombing attack on a temporary military camp in Dagestan. On the same day, there was a murder attempt on a high-ranking official in the republic's capital.