Updated at 2:50 a.m. ET Wednesday

A tour bus destined for Mayan ruins in eastern Mexico flipped over on a two-lane highway early Tuesday, leaving a dozen people dead and many more injured.

Among those hurt were seven Americans and two Swedish tourists, according to a spokesman for the Quintana Roo state Civil Defense agency, which also said it was looking into the cause of the crash.

In a statement from government officials in the Mexican state of Quintana Roo, where the accident occurred, report there were 11 passengers and a tour guide killed. Among the passengers who died was a girl under 18. At least 20 others were injured.

The Associated Press reports: "The bus ended up on its side in vegetation along the two-lane road. Video taken after the crash showed some survivors lying on the pavement and others walking around. One body lay on the roadside covered by a white sheet or other object, as the crash scene was cordoned off with yellow police tape."

A U.S. Embassy spokesman in Mexico City said officials were en route to the scene of the accident, about 100 miles from Tulum. But he could not confirm the number of Americans involved in the deadly incident. The official added that those in need of medical attention had been transferred to several nearby hospitals.

The embassy expected to "have eyes on the ground before the end of the day," according to the spokesman.

Embassy officials issued a statement expressing condolences "to all those affected by this tragedy."

It said, "We are in contact with local authorities and are working with them to determine if there were U.S. citizens on board. We will continue to monitor the situation."

Nearly all the passengers aboard the bus were also passengers on two Royal Caribbean cruises — the Celebrity Equinox and Serenade of the Seas — which set off from Miami. The cruise ship company contracted the local tour bus that was headed out on a day-long adventure to ancient Mayan ruins in Chacchoben.

Royal Caribbean's corporate offices expressed their sadness over Twitter calling the loss of life "heartbreaking" and assured readers the company was assisting with medical care and transportation.

The company also said it had little information about the details of the accident. "Our 27 guests were on a bus tour to the Chacchoben Ruins. We are working with the local authorities to learn more about the accident. We are doing all we can to help our guests."

Photos and video taken in the aftermath of the accident show the bus on its side, pushed up against a thick brush of trees. Beach towels and bottles of water are strewn across the road.

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