Masked thieves have raided an abbey in Ireland and stolen a Christian relic which is said to be part of the cross on which Jesus was crucified, police said today.

The relic, held in a 14th-century silver artefact, has been an object of devotion since around 1180, the priest at Holy Cross Abbey in County Tipperary said.

Father Thomas Breen appealed for the thieves to return the foot-high (30 centimetre) relic, which he said was of little commercial value but had "immeasurable worth in religious devotional practice".

A foot-high gold and bronze cross standing on its own base and containing a centrepiece that could hold the Host was also stolen in the brazen raid.

Two men with their faces covered entered the abbey with an angle grinder, a hammer and screwdriver, and were then seen coming out shortly afterwards and making off in a jeep driven by a third gang member, police said.

Breen said the church had been concerned about security following the disappearance of three sets of keys three weeks ago, including the key to the secure steel cabinet holding the relic.

A locksmith had replaced all the locks last week, but the thieves cut through the cabinet.

"The local community and the friends of the abbey are totally devastated today," Breen told RTE radio, adding that he was shared their devastation.

The local archbishop, Dermot Clifford, said the theft was an "outrage" and appealed for the relic's return.

"The sacred relic is a portion of the True Cross upon which Our Lord was crucified... The unlawful removal of this relic is regarded as an outrage by the people of faith who value its spiritual and historic importance," he said.

Breen said the relic was presented to the abbey by an Irish king, Donal Mor O'Brien, some time around 1180.

"It quickly became a source of devotion and pilgrimage and has remained so for the last 900 years," Breen said.