MEXICO CITY — Authorities said Sunday that a crude explosive device caused a ferry blast that injured more than two-dozen people last month in Playa del Carmen, where the U.S. Embassy has warned travelers to stay away from the ferries and parts of the Caribbean resort city.

Prosecutors said they believe there is no motivation for a terrorist group to have carried out the attack and also think criminal gangs would not have done it, knowing it would draw unwanted attention and increased security.

"Responsibility by terrorist organizations or organized crime has been ruled out," Deputy Attorney General Arturo Elias Beltran said at a news conference.

He added that the bomb "had a very limited capacity" and "was not intended to do major damage."

The Feb. 21 explosion ripped through the upper section of the ferry as it was moored to the dock at Playa del Carmen, leaving a gaping hole in the side of the vessel.

Passengers had already unloaded after making the trip from the nearby resort island of Cozumel but were on the pier at the time. Twenty-six people, including American tourists, were injured — none seriously.

The federal Attorney General's Office said via twitter that on Feb. 19 a person it did not identify went to the naval station on Cozumel to turn in a device consisting of a length of white PVC pipe containing cardboard tubes with cables connected to a black box.

"As a result of the investigations, it can be concluded that the remnants of the explosive artifact (in the Feb. 21 incident) show similarity to the one discovered days earlier, and it is clear that it was a rudimentary or homemade artifact," the office said.

On March 2, another object said to be a possible bomb was found attached to the underside of a ferry belonging to the same company whose boat was bombed earlier. That vessel was anchored about 500 yards (meters) off Cozumel. There were no passengers aboard at the time, and authorities said it had been out of service for over 10 months.

Investigators are pursuing multiple lines of inquiry but have not made any arrests or advanced a definitive theory about a motive for the explosion.

In the wake of the ferry incidents, the U.S. Embassy barred U.S. government workers from taking ferries between Playa del Carmen and Cozumel and warned American travelers to do the same.

The embassy also put out a separate alert, which it said was based on a different, unspecified "security threat," that prohibits U.S. government employees from traveling to five neighborhoods in and around a central tourist zone of Playa del Carmen. Several all-inclusive resorts outside that area are not off-limits, however.

With the spring holiday season kicking into high gear, Mexican authorities sought to reassure travelers that it is safe to visit the Caribbean resorts, a major tourist draw for the country.

Some 60 police officers and sniffer dogs have been deployed to guard the docks and ferries between Playa del Carmen and Cozumel.

Federal Police Commissioner Manelich Castilla said 900 agents have been sent to patrol highways, airports and tourist facilities in Quintana Roo state, which is home to Playa del Carmen, Cozumel, Cancun and Tulum.

He added that hotel occupancy is normal in the state, which receives 19 million visitors each year, half of them from abroad.

"There have not been cancellations of reservations and ... the beaches, without exception, are open without incident," Castilla said at the news conference.

Also Sunday, soldiers and state and federal agents removed the local police force in Tlaquepaque, a large suburb of Guadalajara, Mexico's second city. Officials cited suspicions of infiltration by organized crime.

Tlaquepaque is known for its colorful, well-preserved colonial core and is a popular day trip for tourists staying in Guadalajara.

Jalisco state Gov. Aristoteles Sandoval announced that the Tlaquepaque police headquarters was seized in a morning operation along with weapons and other equipment. The local officers were sent to a police academy for evaluation and training and will be replaced for the time being by state authorities.

Such interventions typically happen when a local police force is believed to be in league with drug cartels. Last month Jalisco authorities took over policing in the town of Tecalitlan, where three Italian men disappeared shortly after some sort of run-in with officers.

"This represents a devastating blow against the insecurity afflicting the metropolis," Sandoval said on Twitter.

"It must be said that the country is suffering from an unprecedented wave of violence. ... Jalisco is not isolated from what the country is going through," he added.

Guadalajara is said to be the home base for the violent Jalisco New Generation cartel.