The chief minister of Gibraltar is "significantly angry" that he was not told about a British nuclear submarine docking for repairs on the Rock.
The Sceptre's docking has angered Spain and Gibraltar
Peter Caruana said he was upset that he found out about the HMS Sceptre from the Spanish foreign minister - who has made an official protest to the UK.
The Ministry of Defence said the stop-off was scheduled and the repairs unconnected to the nuclear system.
Madrid wants the Rock returned to Spain but Gibraltarians want to stay British.
Mr Caruana said: "Our anger is on the basis that the Spanish government were told more and much more quickly than the Gibraltar government were about the exact nature of the repairs that HMS Sceptre was undertaking.
Cause of concern
"We don't believe that it is acceptable that the Spanish government should get preferential treatment," he said.
HMS Sceptre arrived in Gibraltar, at the southern tip of Spain, on Thursday and is due to leave on 9 February.
But visits by UK submarines have been a cause of concern for Spain.
HMS Tireless needed repairs to a pipe near its nuclear reactor in 2000 and stayed on Gibraltar for almost a year.
There were fears the damage could have caused a leak and contaminated the environment.
Spanish Foreign Minister Miguel Angel Moratinos admitted on Friday this visit could not be compared to that of HMS Tireless.
He told Spanish television the breakdown was purely in the diesel engine's cooling systems and not the submarine's nuclear system.
But he added: "We have asked that no more nuclear submarines be given repairs for this kind of breakdown in future, whatever their nature or scale."
A UK Ministry of Defence spokesman said HMS Sceptre was taking advantage of a scheduled stop to carry out repairs.
Last year marked 300 years of UK rule of the Rock.