They say they have discovered a mural depicting the Maya creation myth and the coronation of a king, thought to be more than 2,000 years old.

Archaeologist William Saturno said it was like finding the Maya equivalent of the Vatican's Sistine Chapel.

The mural was discovered at the San Bartolo site in northern Guatemala.

'Unique' find

Mr Saturno, of the University of New Hampshire, said the mural - painted in greyish blue, orange and flesh tones - was discovered at the western wall of a room attached to a pyramid.

An illustration of a cut-out view of the pyramid complex at San Bartolo (Image: Vlad Dumitrascu/©National Geographic)

The mural on the wall - measuring 0.9x9m (3x30 ft) - includes four deities, which are variations of the same figure, the son of the maize god, offering a blood sacrifice from his genitals.

The first deity stands in the water and offers a fish, establishing the watery underworld, Mr Saturno said.

The second stands on the ground and sacrifices a deer, establishing the land; the third floats in the air, offering a turkey to establish the sky; and the fourth stands in a field of flowers, the food of gods, establishing paradise.

The crowned Maya king is depicted at the end of the mural, Mr Saturno said.

"It was like discovering the Sistine Chapel if you didn't know there had been a Renaissance," Mr Saturno said at a news conference.

"It's like knowing only modern art and then stumbling on the finger of God touching the hand of Adam," he said.

Mr Saturno first reported the discovery of the site in 2002.

The western wall is thought to be painted about 100 BC, but was later covered when the room was filled in.

Archaeologists say the artwork is particularly unique because it dates from hundreds of years before the classical Maya period.

The Mayas - known for their prowess in astronomy and mathematics - dominated southern Mexico and parts of Central America for some 1,500 years.

The mural and William Saturno's research will be featured in the January issue of National Geographic magazine.