Congressmen from Argentina and Chile on Friday set aside past differences between their own countries to join in rejecting British claims over Antarctic territory and seabed.
Britain announced in 2007 that it planned to claim sovereignty over a slice of Antarctic seabed that overlaps with areas claimed by Argentina and Chile.
Eight Chilean and two Argentine lawmakers met together at their Antarctic bases and issued a statement saying they "do not recognize the basis" of the British claim.
They expressed support for their governments' efforts "to preserve our rights over the Antarctic continental shelf."
Chile and Argentina have a long history of territorial disputes in the southernmost reaches of South America. The neighboring nations were on the brink of war in 1978 over three mall islands when mediation by Pope John Paul II helped defuse the tensions.