British warships arrived in Gibraltar on Monday for scheduled exercises amid tensions with Spain over fishing around the British Mediterranean enclave.
Although British, Spanish and Gibraltarian authorities have said the navy's arrival at the British overseas territory is long-scheduled, some in Spain see it as provocative.
At about 0800 GMT (4:00 a.m. EDT) the frigate HMS Westminster sailed into the port of Gibraltar flanked by two smaller ships.
It was followed an hour later by the auxiliary ship Lyme Bay, part of a task force of four warships and five other vessels that left Portsmouth and Plymouth about a week ago for exercises in the Mediterranean and the Gulf with various allies.
Gibraltar's creation of an artificial reef with concrete blocks, which Spanish fishermen say blocks their access to certain waters, has prompted Spain to toughen its border checks, leading to long queues for workers and tourists entering Gibraltar.
Spain claims the territory, population just 30,000, which it ceded to Britain by treaty 300 years ago.
In Monday's German Sueddeutsche Zeitung, Gibraltar Chief Minister Fabian Picardo accused the Spanish government of creating conflict to distract attention from corruption allegations against the ruling People's Party.
"In the 19th century, gunboats were used to do politics," he said.
"Today our aim is to improve the living conditions of our citizens by means of cooperation. Unfortunately, Spanish politicians are currently bringing the situation to a head and therefore making things worse for their own citizens in the surrounding regions."
Picardo said the concrete reef was necessary to help marine life recover from overfishing.
As well as tightening border controls, Spain has threatened to charge tourists a 50 euro ($67) border levy, restrict the use of Spanish air space or block Gibraltar's lucrative ship fuelling business.
While Spain has threatened to take its claim to Gibraltar to the United Nations, Britain has asked the European Commission urgently to send monitors to verify whether the border checks breach EU rules.