Spain's Queen Sofia has cancelled a trip to London later this week to attend Queen Elizabeth II's Diamond Jubilee celebration lunch due to tensions with Britain over the disputed territory of Gibraltar.
"The government considers it is hardly adequate that in the current circumstances, Queen Sofia take part in Queen Elizabeth's jubilee," a spokesman for the royal household said overnight NZ time.
A spokesman for the British Foreign Office said: "The visit was a private commitment and we don't comment on private visits."
Last week Spain protested to Britain over a planned visit by Britain's Prince Edward and his wife Sophie Rhys-Jones to Gibraltar from June 11-13.
In talks with Britain's ambassador in Madrid Giles Paxman, Spanish foreign ministry official Santiago Cabanas "expressed how upset and uncomfortable" Madrid is with the visit, the ministry said in a statement.
Prince Edward's visit is part of celebrations to mark the 60th year on the British throne of Edward's mother, Queen Elizabeth II.
There have also been tensions in recent days between Madrid and London over the right of Spanish fishermen to cast their nets in waters near Gibraltar.
Originally both Queen Sofia and her husband King Juan Carlos had been scheduled to attend Queen Elizabeth II's official Diamond Jubilee celebration lunch at Windsor Castle on Friday.
But after King Juan Carlos underwent hip replacement surgery last month following a fall during an elephant hunting expedition in Africa, the royal palace announced only Queen Sofia would attend.
It is not the first time that Spanish royals have declined invitations from their British counterparts over Gibraltar.
In 1981 King Juan Carlos and his wife skipped Prince Charles's wedding to Diana because they planned to make a stop in Gibraltar while on their honeymoon.
Gibraltar, a largely self-governing enclave complete with British pubs and red telephone boxes nestled under a cliffside at the western neck of the Mediterranean, is a rare diplomatic sore point between London and Madrid.
Spain ceded Gibraltar to Britain in 1713 under the Treaty of Utrecht but has long argued that it should be returned to Spanish sovereignty.
Britain refuses to renounce sovereignty against the wishes of Gibraltarians.
The last British royal visit to Gibraltar was by Edward's sister, Princess Anne, in 2009, which likewise annoyed Spain.