Spain's foreign minister Jose Manuel Garcia-Margallo's proposal of a 50 euro ($66) tax to enter or leave Gibraltar, on the Mediterranean coast, has drawn concern from British prime minister David Cameron and a swift and angry reaction from the British colony's authorities.

"What we have seen this weekend is sabre-rattling of the sort that we haven't seen for some time," Gibraltar chief minister Fabian Picardo said in an interview with Britain's Radio 4. "The things that Mr Garcia-Margallo has said are more reminiscent of the type of statement you would hear from North Korea than from an EU partner," he added.

Reef cause of latest row

In an interview published in Spanish conservative daily newspaper "ABC" on Sunday, Garcia-Margallo complained about Gibraltar's decision to build an artificial reef in surrounding waters to stop alleged incursions by Spanish fishing boats.

The foreign minister said Spain would consider introducing a 50 euro tax to enter or leave Gibraltar and use the money to help Spanish fisherman adversely affected by the reef. He also suggested stopping deliveries of materials needed to build the reef, closing Spanish airspace to restrict some flights and reforming online gambling laws to enable Madrid to rake in taxes, as Gibraltar is home to several large online gambling firms.

British PM seeks explanation

British Prime Minister David Cameron is "seriously concerned" by the reports about the border fees and closing Spanish airspace to planes using Gibraltar's airport, his spokesman said on Monday.

"We are seeking an explanation from them (the Spanish government) regarding the reports that they might target Gibraltar with further measures," the spokesman told reporters.

Gibraltar chief minister Fabian Picardo told BBC radio that such fees would violate European Union freedom of movement rules, and said "hell would freeze over" before the reef would be removed.

It is the latest in a string of spats going back decades between Spain and Britain over Gibraltar, the territory known as the "Rock". The diplomatic disputes are frequently sparked by disagreements over fishing rights around the British outpost, which Madrid wants to reclaim as its own.

Spain ceded Gibraltar to Britain in 1713 under the Treaty of Utrecht but has long argued that it should be returned to Spanish sovereignty. Britain refuses to do so against the wishes of the colony's residents. Spain closed the frontier crossing with Gibraltar, which is just 6.8 square kilometers in size (2.6 square miles) and home to about 30,000 people, in 1969. It was fully reopened only in 1985.

se/rg (AP, Reuters, AFP)