MEXICO CITY — Surprised tourists found their little piece of Cancun beach paradise ringed by crime-scene tape and gun-toting sailors last week.

Environmental enforcement officers backed by Mexican navy personnel on Thursday closed off hundreds of feet of powder-white coastline in front of a hotel accused of illegally accumulating sand on its beach.

Mexico spent $19 million to replace Cancun beaches washed away by Hurricane Wilma in 2005. But much of the sand pumped from the sea floor has since washed away, leading some property owners to build breakwaters in a bid to retain its sand. The practice often merely shifts sand loss to beaches below the breakwaters.

"Today we made the decision to close this stretch of ill-gotten, illegally accumulated sand," said Patricio Patron, Mexico's attorney general for environmental protection. "This hotel was telling its tourists: 'Come here, I have sand ... the other hotels don't, because I stole it.' "

Patron said five people were detained in a raid for allegedly using pumps to move sand from the sea floor onto the beach in front of the Gran Caribe Real Hotel.

The hotel is also suspected of illegally building a breakwater that impeded the natural flow of sand onto other hotels' beaches, he said.

An employee of the hotel's marketing office said nobody was available to comment on the allegations.

Authorities said the hotel owner ignored previous orders to remove the breakwater.

A knot of angry tourists gathered around the closed beach.

Some were irked by the sight of police tape and "Closed" signs.

Maria Bachino, a travel agent from Rocha, Uruguay, said by telephone that she had booked a beachfront room in Cancun, only to find herself cut off from the clear, bathub-temperature waters that lure millions to Cancun each year.

"They promised us a beach," said Bachino.

"I apologize to the tourists for this problem, but it is a question of enforcing the law," Patron said.