Brazil has defended its decision to allow British Royal Air Force flights to use its territory for stopovers on their way to and from the Falkland Islands, after Argentina complained.

"Brazil supports Argentina's legitimate rights in its sovereignty dispute" with Britain over the islands, the Brazilian foreign ministry said in an email sent to AFP.

However, that "does not affect relations with the United Kingdom, an important partner for Brazil," it added.

The reaction came after Argentina's ambassador to Brazil sent a formal complaint over the flights on January 31.

Ambassador Daniel Scioli said there had been seven such flights in January, which he wrote caused "surprise and concern" in Argentina.

The stopovers "are another sign of the United Kingdom's illegitimate military presence in the South Atlantic," the letter said.

It called on Brazil to "restrict authorization for British military aircraft flying to or from (the islands) to strictly humanitarian cases."

Brazil said its decision to allow the stopovers was "guided by the principle of not contributing to the modernization and expansion of the United Kingdom's military resources and potential in the archipelago."

It said the January flight authorizations were based on "emergency situations, search and rescue missions, and health and humanitarian reasons."

Argentine diplomatic sources told AFP there had been no official reply from Brazil to the complaint.

Argentina, which calls the archipelago the Malvinas Islands, fought and lost a brief but bloody war with Britain over the territory in 1982.

Buenos Aires argues it inherited the windswept islands from Spain when it gained independence in the 19th century.

Britain says it has historically ruled them and that the islanders -- who number around 3,000, most of British descent -- should have the right to self-determination.

In a 2013 referendum, residents voted overwhelmingly to remain part of Britain.