The four journalists were kidnapped on Monday after covering a prison scandal in the northern state of Durango in which inmates are accused of being hired guns for a local drug cartel.

Attacks on the media have mounted as drug gangs seek to silence journalists who report on the drug-related killings.

Since 2006, at least 30 journalists have been killed in Mexico, according to Mexican media.

Mexico is considered to be one of the world's most dangerous countries for the media.