At least 16 police officers have been  wounded after gunmen launched a string of attacks on police bases throughout the western Mexican state of Michoacana, a stronghold of the country's drug cartels. The attackers were armed with grenades and assault rifles.

In one incident, in the state capital Morelia, 40 gunmen arrived in a convoy of vehicles to execute the raid. In another incident, three police officers were gunned down on the street when they were attending to a car crash.

The onslaught is seen as retribution for the arrest of a senior member of La Familia drug cartel, Arnoldo Rueda, on Friday. Mexican authorities say the attack is one of the most violent ever by drug cartels.

Mexican President Felipe Calderon had deployed some 36,000 troops and policemen in a bid to stem the drug violence, which has claimed the lives of  more than 7,000 people since 2008.

Photo of a victim of the Mexican drug war by Federacion de asociaciones cannabicas (flickr)