SANTIAGO, Chile (AP) -- A bus carrying tourists from a cruise ship plunged into a ravine Wednesday in the highlands of northern Chile and officials said 11 people were killed, most believed to be U.S. citizens.

The bus was carrying tourists from a Bahamas-registered Millennium cruise ship for a visit to a national park outside of Arica, a city 1,250 miles north of Santiago, near the border with Peru and Bolivia, said Juan Carlos Poli, a municipal spokesman for Arica.

Poli said an undetermined number of tourists were injured in the accident. Regional governor Patricia Perez said a preliminary report by police put the number hurt at 5.

"Rescue crews are working in the area, but we have confirmed 11 people killed, most of them apparently from the United States," Poli said.

The bus had a capacity for 54 passengers, but Poli said it was not immediately known how many people were on board.

The accident occurred about 28 miles northeast of Arica on the road to the Bolivian capital city of La Paz.

"We still do not know the cause of the accident, but the road passes several cliffs and is very curvy ... a dangerous road," Poli told The Associated Press by telephone.

The tourists were returning to the ship, which had arrived in Arica earlier in the day, after visiting the Chungara Lake in the Lauca National Park, at an altitude of 13,000 feet