About 200 gunmen reportedly massacred and decapitated at least 27 people in northern Guatemala Sunday.
Police told the Los Angeles Times the gunmen attacked workers on a coconut farm in Peten province, an area into which Mexican drug smugglers have been active.
The gunmen reportedly arrived in buses and decapitated 25 men and two women.
"This is the worst massacre we have seen in modern times," police spokesman Donald Gonzalez told Reuters.
Police did not yet have a motive but were investigating a link to the killing a day earlier of a brother of a widely known suspected trafficker. Haroldo Leon was killed Saturday. He is the brother of slain suspected drug trafficker Juan Jose Leon.
A national civil police spokesman, Moises Ical, told the Miami Herald the killings were related to drug trafficking. He said a suspect is the Los Zetas gang, which operates freely in much of the region.
"We have neither the personnel nor the means to fight these drug traffickers," Ical said.
Drug smugglers use illegal border crossings in the jungle region.
Los Zetas are former soldiers who were originally hit men for Mexico's Gulf drug cartel.
"The brutality of the killings and beheadings is a trademark of Los Zetas, which is engaged in a turf war in northeast Mexico with the Gulf Cartel. Even as Los Zetas have appeared on the ropes in Tamaulipas state in Mexico, they have moved strongly into Guatemala and Honduras, diplomats and law enforcement officials say," the Miami Herald states.