British Foreign Secretary Boris Johnson laid a wreath to honor Argentine soldiers killed while fighting the British in the 1982 Falkland Islands conflict.
Johnson, who is in Buenos Aires for a Group of 20 meeting, visited the Monument of the Fallen Soldiers on Sunday along with Argentine Foreign Minister Jorge Faurie.
Argentina, which has claimed the South Atlantic islands since Britain established its rule in the 19th century, invaded them in 1982, sparking a two-month war that ended with Argentina's defeat and withdrawal from the archipelago.
Johnson is only the second senior British official to pay tribute to the 255 British and 649 Argentine soldiers who died during the 74-day conflict.
Prince Charles visited so at the same monument during a visit in 1999.
Britain and Argentina are both keen to strengthen ties and recently held talks over fishing rights around the islands, 500 kilometers off Argentina's southern coast.
The two nations don't even agree on a name for the islands, with Britain referring to them as the Falklands and the Argentines calling them Malvinas.