Both territories -- the Falklands in the South Atlantic, which Argentina calls the Islas Malvinas, and Gibraltar at Spain's southern tip -- are controlled by Britain.
But Argentina and Spain claim sovereignty over them, respectively.
The agreement to work together in dealing with Britain came after Argentine Foreign Minister Hector Timerman met with his Spanish counterpart Jose Manuel Garcia-Margallo on the sidelines of the UN General Assembly.
The agreement was reported by the Argentine Foreign Ministry in a statement that said the two countries noted similarities in their respective disputes with Britain.
London says it will not do so against the wishes of Gibraltarians, who are staunchly pro-British.
Argentina and Britain fought a brief but costly war over the Falklands in 1982. Argentina lost. The fighting left 649 Argentines and 255 Britons dead.
