Cameron refused the handoff, which was offered to him in a corridor at the summit meeting in Los Cabos, Mexico, The Independent reported. Instead, he told Fernandez her attempts to bring the Falklands up at the United Nations were "unacceptable."
Both countries claim the island group, called the Malvinas by Argentina. Thirty years ago, Britain beat back an Argentine attempt to seize the Falklands.
Fernandez refused to accept a letter from residents of the islands at the U.N. The island government said recently it plans a referendum next year that is expected to result in an overwhelming vote to remain British.
Witnesses said Fernandez's confrontation with Cameron appeared designed to be filmed. The envelope had both Malvinas and United Nations written on the outside in large letters.