Mexican vigilantes vow to "end the life of a criminal every 24 hours."

Shadowy vigilante groups are threatening Mexico's drug gangs near the U.S. border in retaliation for a wave of murders and kidnappings that killed 1,600 people in this city alone last year.

One group in the border city of Ciudad Juarez pledged last week to "clean our city of these criminals" and said their mission was to "end the life of a criminal every 24 hours."

The emergence of vigilantes would be a new twist to a vicious drug war that killed 5,700 people in Mexico last year and forced the United States to give hundreds of millions of dollars in aid to the Mexican government.

Ciudad Juarez, a manufacturing center in the desert across from El Paso, Texas, was the scene of the worst violence in 2008 as drug cartels fought each other as well as staging kidnappings for ransom and extorting businessmen.

In an e-mail to news organizations, the "Juarez Citizen Command" said it was funded by local businessmen sick of abductions and extortion in the city, home to factories that export goods to the United States.

While none of the city's 1,600 in the last year were undoubtedly the work of vigilantes, a body was found on Jan. 7 with a message next to it that read: "This is for those who continue extorting."

And six men in their 20s and 30s were shot dead and dumped together in Ciudad Juarez in October with a cardboard sign reading: "Message for all the rats: This will continue."