Guadalajara, Mexico (CNN) -- Authorities found more than 20 bodies inside three abandoned vehicles in Guadalajara, Mexico, Thursday, state media reported.

The vehicles were discovered near a monument on one of the city's main avenues, the state-run Notimex news agency said, citing police sources.

Officials did not release the exact number of bodies found Thursday morning.

Jalisco state Attorney General Tomas Coronado Olmos told CNN affiliate TV Azteca that a message was found with the bodies, but he did not disclose what it said.

In a Twitter post, Jalisco Gov. Emilio Gonzalez -- a former mayor of Guadalajara -- said he was "appalled and outraged" by the discovery.

About 43,000 people have been killed in drug-related violence since Mexican President Felipe Calderon announced a crackdown on cartels in December 2006, according to the U.S. Drug Enforcement Administration.

But brutal cartel killings are rare in Guadalajara, Mexico's second-largest city.