The Royal Navy has fired a warning shot at a Spanish patrol boat as it tried to 'hassle' a US nuclear submarine attempting to dock at Gibraltar, it has emerged.

Spanish Guardia Civil vessel Rio Cedena twice tried to disrupt the visit by ballistic missile sub USS Florida as it was approaching the British Overseas Territory on the southern tip of Spain.

Flares were fired across its bow as it sailed in front of the American submarine and the Royal Navy reportedly dispatched its squadron patrol vessel HMS Sabre.

Spanish Guardia Civil vessel Rio Cedena twice tried to disrupt the visit by ballistic missile sub USS Florida (shown in this file picture) as it was approaching the British Overseas Territory on the southern tip of Spain

Flares were fired across the bow of a Spanish Guardia Civil (file picture) as it sailed in front of the American submarine

According to the Sun, the incident has caused outrage among senior officials in Gibraltar with one 'top source' saying: 'This is not only a very dangerous game for the Spanish to play but it is unbecoming of a NATO ally to treat the US Navy with such contempt.'

The newspaper reports that the incident happened in mid-April and senior Royal Navy sources have confirmed the flare firing.

A Ministry of Defence spokesman told MailOnline this morning: 'We don’t comment on force protection measures or submarine operations.'

The Sun reported that a spokesman for Gibraltar's Governor’s office as confirming the incident.

It is not the first time such incursions have been reported.

In August, the Government of Gibraltar said they were 'astonished and appalled' after Spanish police used boats and helicopters to make several incursions into British waters.

The Royal Navy reportedly dispatched its squadron patrol vessel HMS Sabre (file picture) when the incursion took place

The incident happened as a US Navy submarine was approaching Gibraltar during a visit

A year earlier HMS Sabre was embroiled in a stand-off with Rio Cedena after another illegal incursion.

Britain was given Gibraltar in the 1713 Treaty of Utrecht, but Spain has said it will never renounce its claim to sovereignty.

Spanish aggression over the Rock increased after the election of Mariano Rajoy as the country’s prime minister in 2011.

But relations between Madrid and London over the Mediterranean territory have deteriorated drastically since the construction of an artificial reef by the Gibraltar government which Spain says has interfered with their fisherman.

Madrid responded by imposing tighter border controls, leading to long delays at the frontier, as the row escalated.