Gibraltar is pleased that Spain is "at last" thinking of taking its longstanding dispute over the sovereignty of the British outpost to international courts, Gibraltar Chief Minister Fabian Picardo told Agence France Presse in an interview Wednesday.

Picardo also accused Spanish Prime Minister Mariano Rajoy's Popular Party government of trying to divert attention from a corruption scandal with a dispute over an artificial reef built by Gibraltar.

Drivers fumed in hours-long queues Tuesday to cross into the tiny British outpost of Gibraltar from Spain as tensions mounted between Madrid and London over the disputed territory.

"At present the incoming queuing time is over three hours. All documents being checked," the Royal Gibraltar Police said in a Twitter message.

Spain will take "all necessary measures" to defend its interests in Gibraltar, Prime Minister Mariano Rajoy said on Friday amid a row with London over the British outpost on Spain's southern tip.

"We will take legal measures which are proportionate to defend the interests of Spaniards," he said after a meeting with Spain's King Juan Carlos on the Mediterranean island of Majorca.

British Prime Minister David Cameron on Wednesday warned his Spanish counterpart that the escalating tit-for-tat over border tensions in Gibraltar risked damaging relations between their countries.

Cameron and Mariano Rajoy discussed ways to calm the situation in a call Britain described as "constructive" after tensions rose at the weekend when Spanish Foreign Minister Jose Manuel Garcia-Margallo threatened to impose steep tolls to cross the border.

The European Commission said Tuesday it would send a team of monitors to the Spain-Gibraltar border as perennial frontier spats resurfaced.

Commission spokesman Frederic Vincent said the EU "has informed the Spanish authorities of our intention to send Commission experts to the border."

The tiny British-held territory of Gibraltar complained to the European Union Thursday over delays at its border crossing with Spain which it said were "deliberately" caused by Spanish authorities.

Over the weekend the government of Gibraltar said cars entering and leaving the territory on Spain's southern tip were made to wait up to six hours to cross the border as Spanish authorities searched "practically every vehicle".

Spain has eased intensive checks on the Gibraltar border that caused delays to car traffic but Britain will be "closely monitoring" the situation, Prime Minister David Cameron's spokesman said Monday.

London has raised concerns with Madrid after Gibraltar's government said vehicles leaving the British-held territory on Spain's southern tip had been made since Friday to wait nearly six hours to get through new security inspections.

Spain flatly denied Wednesday allegations that its police shot at a jet ski in waters off Gibraltar and criticized Britain for giving credence to rumors.

The alleged incident on Sunday off the disputed rock has escalated into a diplomatic row.

Britain summoned the Spanish ambassador to London on Thursday to complain about "serious incursions" in the waters off the British Mediterranean enclave of Gibraltar, officials said.

Junior foreign minister David Lidington said recent attempts by Spanish officials to exercise jurisdiction in Gibraltar's territorial waters were "provocative" and risked damaging ties between Gibraltar and Madrid.