David Cameron has protested to his Spanish counterpart after shots were fired at a jet skier off the coast of Gibraltar.
The Prime Minister confronted Mariano Rajoy during a Brussels summit and demanded an explanation for the "illegal incursion" into British territorial waters.
Mr Cameron said at a press conference that he wanted to make sure a full investigation took place, adding it was important that countries follow international law.
He said: "I did raise this with the Spanish Prime Minister. I think this is a totally unacceptable episode and I made that clear.
"I think it is very important that people on Gibraltar know that we support them, we support their sovereignty".
During the incident, which took place on Sunday, a Spanish police boat pursued Dale Villa while he was on his jet ski near West Beach.
Witnesses reported seeing a large number of plastic batons being fired from the Guardia Civil vessel. No one was injured.