Britain has protested to Argentina over its interception of UK-licensed fishing boats in disputed waters near the Falkland Islands, over which the two countries went to war in 1982.
Last year, Argentina passed a decree requiring ships sailing between the Falklands, South Georgia and the nearby South Sandwich Islands to obtain permission to pass through Argentine jurisdictional waters.
The Falklands government issues licences to vessels wanting to fish inside a 200-mile maritime zone around the islands.
In the latest series of incidents, soldiers on Argentine patrol boats intercepted radio communications of Spanish fishing vessels operating with UK licences and asked for information from the captain.
On a number of occasions in recent months the Argentine coast guard and navy have challenged boats travelling between the Falkland Islands and the port of Montevideo in Uruguay, said Mike Summers, a member of the Falkland Islands legislative assembly.
They hail the boats and ask them for information such as the passport number of the captain, possibly trying to warn them off.
He said interceptions had not led to a disruption of trade.
The British Foreign Office said in a statement: The UK has protested to Argentina ... We consider that it is not compliant with international law, including the United Nations Convention on the Law of the Sea (UNCLOS).
Britain and Argentina fought a 10-week war over the Falkland Islands after Argentina invaded the South Atlantic islands during Margaret Thatcher's reign as British prime minister.
Despite the British victory, Argentina continues to claim Las Malvinas as its own.
Last month it accused Britain of acting provocatively by announcing that Prince William, second in line to the throne, is expected to be deployed to the Falklands in February as part of his training duties with the Royal Air Force.
In October, then Defence Secretary Liam Fox said Britain would protect the 3,000 people of the islands for as long as they want to remain British citizens.
(Reporting by Philip Baillie)