The tiny British-held territory of Gibraltar, known as The Rock, has protested to British Prime Minister David Cameron of repeated Spanish incursions into its waters as a diplomatic row grows over allegations that Spanish police fired shots at a jet ski.
Spain's government has flatly denied accusations that its police fired shots while chasing a jet ski on Sunday in waters off Gibraltar and it has criticised Britain for giving credence to rumours.
As the dispute mounted, Gibraltar Chief Minister Fabian Picardo sent a letter to Cameron, according to a statement late Wednesday by the territory's government.
In it, he complained that Spanish incursions into British territorial waters at Gibraltar "constitute a serious challenge to Gibraltar's jurisdiction and British sovereignty".
Picard said Spanish military-linked Guardia Civil police shot at the jet ski inside British territorial waters, an incident he described as "dangerous and wholly unacceptable".
"Diplomatic action to date appears to have had no material effect and I fear that Spain will not be deterred by yet another verbal protest no matter how robust," he said.
"It is important that Spain feels the true weight of British reaction to continuing violations of our sovereignty."
Britain's Minister for Europe David Lidington protested the "illegal incursion" to his Spanish counterpart during a European Union meeting in Luxembourg on Tuesday.
And the British embassy's number two man in Madrid, Daniel Pruce, has demanded from the Spanish foreign ministry a "full explanation".
But a spokesman for Spain's foreign ministry told AFP there was no shooting and expressed disquiet that Britain was repeating an "unverified and unfounded rumour".
In Gibraltar, the man reportedly at the centre of the incident, 32-year-old David Villa, told online news site Olive Press that he had been testing his new jet ski with family and friends on Sunday when the Spanish police gave chase.
"There were three policemen on the boat and I actually saw one of them with a gun in his hand," he was quoted as saying.
"I was just about to drop my friend off at West Beach when I heard the first shot."
In November, Spain and Britain summoned each other's ambassadors in a spat over a series of naval incidents around the small but strategically situated territory.
Britain has held Gibraltar since 1713 but Spain wants it returned and refuses to recognise British sovereignty over the waters off the land.