PLAYA DEL CARMEN, Mexico -- What appeared to be undetonated explosives were found on a ferry that runs between the Caribbean resorts of Playa del Carmen and the island of Cozumel, authorities in Mexico said Friday, less than two weeks after a blast shook another ferry plying the same route.

Quintana Roo state prosecutor Miguel Angel Pech Cen said in interviews with Mexican media that the boat was anchored 500 yards (meters) from the Cozumel dock and was not in service when the object was discovered Thursday. He said a company diver reported the object, and Mexican navy divers removed it and handed it over to the Defense Department for analysis.

The announcement came on the heels of reports that a Feb. 21 explosion on a ferry owned by the same company and on the same route was caused by a bomb. That blast injured 19 Mexicans and at least five U.S. citizens. Authorities had initially suggested it could have been a mechanical malfunction.

The U.S. Embassy in Mexico said in a statement that it was barring its workers from taking any tourist ferries on that route because "undetonated explosive devices were found" on the boat. The region is one of the most popular travel destinations in Mexico.

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"U.S. Government employees are prohibited from using all tourist ferries on this route until further notice. Mexican and U.S. law enforcement continue to investigate," the embassy wrote.

Photos of the device published in local media showed what appeared to be a length of PVC pipe attached to the underside of a boat.

Pech Cen argued that there was no danger to tourists because the boat was out of service and far from the dock. He noted that the Defense Department had yet to issue a definitive finding on the nature of the object.

The state Tourism Department said the same in a statement and added that the vessel had not been in commercial service for over 10 months. State and federal prosecutors are investigating, it said, "and the cooperation of international agencies such as the FBI is accepted."

Among the lines of inquiry is the possibility that "the incidents are exclusively related to situations that are internal and inherent to the ferry line in question, which is not providing commercial service," the statement said.

"I would say the effect on the tourist population is an undesired collateral effect of something that probably has some other motive," federal Interior Secretary Alfonso Navarrete said.

Except for isolated shootings last year, Mexico's Caribbean coast has largely been spared the violence plaguing other parts of Mexico. The coast provides much of Mexico's tourism revenue.

The ferry company, Barcos Caribe, whose boat was hit by the Feb. 21 blast, was suspended by the government from operating four days later, even though the firm said it had the necessary permits.

Local media have reported the company is owned by the father of former Quintana Roo state Gov. Roberto Borge, who is under arrest on corruption charges.

An employee at the firm said Friday that the company's boats were not currently operating but did not immediately respond to the reports about the firm's links to the Borge family.

Ferries not operated by Barcos Caribe continued to shuttle passengers between Cozumel and Playa del Carmen on Friday.

On Cozumel, tourist Jack Bushman of New York had not heard of the incidents or the U.S. travel alert until a journalist asked him about it.

"I think the Mexican government will probably be doing a good job searching the ships, making sure this doesn't happen again," Bushman said. "They want us all to be safe and travel, and they want us to be here for tourism."

While violence is on the rise in Mexico amid a bloody drug war that is over a decade old, use of explosives to target groups of civilians is rare - with some exceptions.

In 2008, eight people were killed and dozens wounded when a grenade was tossed into the city of Morelia's main square during Independence Day celebrations. In 2011, a casino in the northern city of Monterrey was doused with gasoline and set aflame, killing 52 people.

Drug cartels were blamed for both incidents.