Vandals defecated and urinated in a Londonderry church after breaking in and causing extensive damage to the church's organ.
The break-in was discovered at Christ Church on Infirmary Road late on Tuesday.
A decanter used in Holy Communion was stolen. It is also believed faeces was smeared on the pages of a psalm book.
The Church of Ireland Bishop of Derry and Raphoe, Rev Ken Good, described the incident as "sacrilege".
Police have yet to establish a motive for the attack, which they say happened sometime between Sunday afternoon and Tuesday at about 16:15 BST.
It is believed the vandals broke in through one of the church's stained-glass windows.
The worst of the damage was inflicted on the church's organ, said Robert Miller, the parish's rector.
"They climbed in behind the organ and used broken glass - probably from the bottles of altar wine which they had smashed - to cut parts of the mechanism which makes the organ work."
He added that the organ would be out of action for some time.
"Our church organist was heartbroken when he saw the extent of the damage," he said.
"The instrument was installed in 2000, four years after the previous organ had been destroyed in a fire. So, this latest act of vandalism has come as a severe blow to us."
The vandals also smashed windows, knocked over vases of flowers and removed a bible from a lectern and flung it into the church's sanctuary.
"There seems to be just a mindlessness to it. I don't think there's any sectarian agenda, we just happened to be a place of opportunity," Archdeacon Miller added.
"It's unfortunate that the damage to the stained glass window and the organ are both significant."
Bishop Good said he "felt deeply" for the parishioners of Christ Church.
"I can assure them that the people who would perpetrate such an outrage are small in number and in no way represent the vast, vast majority in our community who want to live in peace and harmony."
Bishop Donal McKeown, the Catholic Bishop of Derry, said the attack appeared to be "opportunistic vandalism".
"I think we just really feel for the comparatively small Church of Ireland community that worships here, a church where we have been so often for ceremonies, for concerts and for events. I think we have a real sense of solidarity with them."
Elisha McCallion, the Foyle MP, said the break-in and vandalism were "disgraceful".
"Those responsible for this mindless attack are not representative of the people of this city and have nothing to offer society.
"My thoughts are with Archdeacon Robert Miller and all the parishioners at Christ Church. I know that this city will rally round and support them in any way we can at this difficult time."
DUP MLA Gary Middleton described it as a "disgusting attack on a place of worship".
"It is important that those who could cause such damage are brought to justice," he added.
SDLP councillor John Boyle said the incident was "repugnant and sickening".