Mexican authorities must investigate the death threat made over the weekend against journalist Lydia Cacho, the Committee to Protect Journalists, or CPJ, said.

"This threat is the latest in a long line of efforts to intimidate Lydia Cacho, one of Mexico's most prominent reporters," CPJ senior program coordinator for the Americas Carlos Lauria said in a statement.

"The delivery of the threat over her own emergency communication system should be particularly alarming to Mexican authorities, who must ensure her safety," Lauria said.

Cacho is an award-winning investigative reporter, human rights activist and columnist for the daily El Universal.

Her latest book, "Esclavas del poder" (Slaves of Power), examined people trafficking and its victims around the world.

The Mexican journalist told the CPJ that the threat was made over the security system at her house in the Caribbean resort city of Cancun, the press rights group said.

"Cacho said an unfamiliar voice came over the system's speaker on Sunday, warning her 'not to mess with us' or 'we will send you home in little pieces.' Her security consultants believe the individual had used advanced technology to gain access to the system," the CPJ said.

The Mexican journalist told Efe in early July that the death threats she received by telephone on June 17 and in the mail a few days earlier would not silence her because her voice was the best weapon against fear.

"They want to silence my work and defense of the rights of women because they know we have them tied up, but they will not succeed," Cacho told Efe after an event in Mexico City on July 6.

The journalist has been the target of threats since 2005, when she published a book, "Los demonios del Eden" (The Demons of Eden), that exposed pedophile rings in Mexico operating under the protection of politicians and business leaders.

For revealing the crimes of Lebanese-born Mexican businessman Jean Succar Kuri and others, Cacho was the victim of kidnapping, psychological torture and police abuses, which she revealed in another book titled "Memorias de una infamia" (Memoirs of an Infamy).

Mexico, where nearly 80 journalists have been murdered since 2000, is considered one of the most dangerous countries in the world for members of the media. EFE