Image caption The thieves tried to take several petroglyphs but aborted and left them badly scarred

Saw-wielding thieves have stolen a series of ancient carvings from a California cliff side.

At least four of the carvings, known as petroglyphs, were taken over a period of several hours, US officials said, with others badly defaced.

The petroglyphs are thought to have survived for thousands of years at the desert site near Bishop, California.

Petroglyphs, or rock engravings, are created by removing the surface layer of rocks to reveal the colours below.

They are usually of prehistoric origin, and can be found at ancient sites around the world.

Their culture and spiritual beliefs had been horribly violated. We will do everything in our power to bring those pieces back Bernadette Lovato, US Bureau of Land Management

'Worst vandalism'

The carvings vandalised in the Volcanic Tablelands area of California vanished from a site on land held sacred by the Paiute-Shoshone tribe in the Sierra Nevada mountain range, near the Nevada state line.

The extent of the theft - as well as the amount of damage inflicted on other carvings left in place - prompted a sombre verdict from the US Bureau of Land Management (BLM), which administers the area.

"This was the worst act of vandalism ever seen" on BLM land, archaeologist Greg Haverstock told the Los Angeles Times.

At least four of the petroglyphs have gone, while a fifth was defaced with deep cuts on its sides. A sixth carving was removed and broken before being propped against a boulder near a visitor's car park.

Image caption Intact petroglyphs still adorn rock faces around the world

The thieves are said to have gone to extraordinary lengths to destroy the site.

They used ladders, electric generators and power saws and gouged holes in slabs of rock that were up to 5m (15ft) above ground.

The authorities say the petroglyphs could be worth up to $1,500 (£950) each on the black market.

But they are priceless to Native Americans. "Their culture and spiritual beliefs had been horribly violated," BLM field office manager Bernadette Lovato told the LA Times.

"We will do everything in our power to bring those pieces back."