Thirteen people were killed in and around the Mexican beach resort of Acapulco, with four victims found beheaded, security officials said. Another gunbattle in the state left 11 people dead.
Five of those killed were police officers whose night-time patrol was ambushed by gunmen early Saturday in Tuncingo, a rural area on the outskirts of the Pacific coast resort city.
The bullet-riddled bodies of eight other men were discovered in different areas around Acapulco in apparent drug-related killings, officials said. Two of the decapitated men were found on a scenic road packed with nightclubs.
The violence occurred as thousands of U.S. college students started arriving in the area for spring break.
More violence apparently linked to drugs flared later Saturday in Guerrero state, where Acapulco is located, with Mexican soldiers exchanging fire with gunmen, national newspaper Reforma reported. One soldier and 10 gunmen were killed in the shootout in the town of Ajuchitlan del Progreso, the newspaper said.
Valentin Diaz, director of the Guerrero state investigative police, said the gunfight erupted in the middle of the day in the center of the town as it was full of bystanders.
Several cartels are fighting over drug-dealing turf and trafficking routes in Guerrero. Gang violence occurs almost every day in the state, but Saturday was unusually bloody.
Any resurgence in violence would be bad news for the country's tourism industry. Last June, at least 18 people were killed in a shootout between drug gangs and soldiers in Acapulco, which is home to around a million people.
President Felipe Calderon has deployed tens of thousands of troops to Guerrero and other drug-trafficking hotspots across Mexico in an effort to root out cartels. Gang violence has surged since the crackdown began three years ago, claiming more than 17,900 lives.
Farther to the south in the state of Chiapas, which borders Guatemala, a grenade explosion inside a car killed one man and wounded another. State prosecutors said the dead man was holding the weapon when it exploded.
Investigators believe the victim belonged to the Zetas drug gang and had been about to throw the grenade at federal police offices in the state capital, Tuxtla Gutierrez.