Garcia-Margallo criticised London's position during an appearance before the Spain's senate Tuesday.
Britain will not discuss ceding sovereignty to Spain without the consent of the residents of the Rock (Gibraltar), Cameron had said Tuesday in a message to mark Gibraltar's National Day.
Madrid, however, said sovereignty is a matter exclusively for the Spanish and British governments, and pointed to a series of UN resolutions dating back to 1965.
"Spain does consider itself obliged by those resolutions, just as by all international legality," Garcia-Margallo said.
Gibraltar, a territory of 5.5 sq. km at the entrance to the Mediterranean Sea, has been held by Britain since 1704 and became a British crown colony in 1713 under the Treaty of Utrecht.
Spanish Prime Minister Mariano Rajoy said last week that his meetings with Cameron during the G20 Summit in Russia "laid the foundation for a dialogue" to address recent bilateral frictions over Gibraltar.
"Obviously, whenever two people talk, it produces a better situation than if those two people don't talk," Rajoy said.
"It's evident that there was a problem and no one had an interest in having problems, and it's evident there has to be dialogue," he added.
While calling for caution, the Spanish prime minister said he was confident the situation "will end well for everyone".
The latest flap over Gibraltar, a British overseas territory sitting at the tip of the Iberian peninsula, began when the local administration on the Rock dropped 70 concrete blocks into the Mediterranean with the aim of forming an artificial reef.
The reef project violates the European Union's environmental regulations and threatens the livelihood of Spanish fishermen, according to Madrid, which imposed new border checks that have led to hours-long waits for people entering and leaving Gibraltar.
Responding to individual complaints from Spain and Britain, the European Commission launched separate probes into the reef project and the new border controls.
--IANS (Posted on 11-09-2013)