The U.S. Embassy in Mexico has narrowed its travel warning for the Caribbean resort city of Playa del Carmen amid what it calls an unspecified "ongoing security threat" just as the spring holiday season is kicking into high gear.

In a notice posted Friday on its website, the embassy also said the U.S. Consular Agency in the city would reopen and resume normal operations Monday after a shutdown of several days — "absent additional changes in the security situation."

The revised restrictions say U.S. government employees must avoid five neighborhoods in and around a downtown tourist zone filled with hotels, restaurants, shops and bars.

Tourists and passengers disembark from a ferry on to the wharf on Playa del Carmen, Mexico, Friday, March 2, 2018. Undetonated explosives were found on another ferry that runs between the Caribbean resorts of Playa del Carmen and the island of Cozumel, authorities said, less than two weeks after a blast shook another ferry plying the same route. (AP Photo/Gabriel Alcocer)

But they lift a blanket ban issued this week for the city that had covered several all-inclusive resorts. The embassy said employee travel is now permitted "to resort areas in Riviera Maya including those near Playa del Carmen that are outside the restricted neighborhoods."

After the first travel alert Wednesday, Mexican officials came out to defend public safety in Playa del Carmen, apparently concerned about a possible hit to tourism in one of the country's most traveled regions.

The Quintana Roo state government noted that President Enrique Pena Nieto and dignitaries from around the globe were convening there for the World Ocean Summit on March 7-9, saying tourist activity was normal in the city with hotel occupancy at 80 percent.

Parts of Mexico's Caribbean coast, which also includes the resorts of Cancun and Tulum, have been hit by drug violence, albeit infrequently, and the Jalisco New Generation drug cartel has been moving into Quintana Roo.

But the exact nature of the new threat was not clear, and the embassy said it was separate from incidents involving ferries on the route between Playa del Carmen and the nearby island of Cozumel.

A Feb. 21 explosion on a ferry injured 26 people including several American citizens. What appeared to be explosives were later found attached to the underside of another vessel operated by the same company, Barcos Caribe.

Both incidents are under investigation.

The U.S. Embassy said government workers are still prohibited from taking ferries between Cozumel and Playa del Carmen, and it recommended that U.S. citizens avoid them as well.