MEXICO CITY (Reuters) - Twelve people died and 18 were injured on Tuesday in Mexico’s state of Quintana Roo when a tour bus lost control and rolled over during an excursion to ancient ruins.

The bus was carrying 31 passengers, including citizens of the United States, Brazil and Sweden, authorities said. A child was among the dead. Quintana Roo is one of three states on Mexico’s Yucatan Peninsula, which has popular tourist sites.

Twenty-seven of the passengers had been traveling on Royal Caribbean cruise ships, spokeswoman Cynthia Martinez said.

“Our hearts go out to all those involved in the bus accident,” Martinez said in a statement. “We are doing all we can to care for our guests, including assisting with medical care and transportation.”

The tourists were headed to the archaeological zone of Chacchoben, an ancient Mayan ruin south of the resort town of Tulum, when the vehicle veered off the highway early on Tuesday.

After the accident, passengers were taken to hospitals, bus company Costa Maya said in a statement. Five have been discharged and the injured were in stable condition, it said.

The government of Quintana Roo said in a statement that it was investigating the cause of the accident.

The U.S. embassy in Mexico said it was working with authorities to learn whether U.S. citizens were aboard the bus.

Last year, 11 tourists were killed in a crash in Quintana Roo when their bus flipped en route to Cancun, the Associated Press reported.