Russian authorities say a police van has been blown up in the southern republic of Dagestan, wounding six officers.

The explosion occurred early Tuesday in a town (Khasavyurt) west of the regional capital, Makhachkala. Two of the wounded policemen are in critical condition.

In a separate development, authorities Tuesday also defused a bomb planted along a highway west of Makhachkala.

There has been no claim of responsibility for either incident. Both Islamic militants and criminal gangs are known to operate in the republic.

A new Russian study found violence has more than doubled in Dagestan in the last year.

Some information for this report provided by AP.