The Times has published pictures of the paintings, some 6,000 years old, showing them defaced with spray paint.

Julian Harston, the UN official responsible for Western Sahara, said he had been shocked by the vandalism.

He said funds would now be sought from the UN cultural organisation, Unesco, to remove the graffiti.

Western Sahara has been at the centre of a bitter dispute since former colonial power Spain pulled out in 1975 and neighbouring Morocco invaded.

UN peacekeepers were deployed in 1991 to monitor a ceasefire between Morocco and the Algerian-backed Polisario Front, which has been seeking independence for the territory.

'Tragedy'

Graffiti, including the spray-painting of UN personnel's names, can be seen at Lajuad, an important archaeological site, Mr Harston said.

According to The Times, an area there known as Devil Mountain is regarded by the local Sahrawi people as a place of great cultural significance.

"I was appalled. You'd think some of them would know better. These are officers, not squaddies," Mr Harston said.

Nick Brook, a climate scientist who runs the Western Sahara Project, has written a blog about his findings which show pictures of graffiti more than a metre high on granite rocks.

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