Fernandez was flying Friday afternoon to a regional summit in Colombia, leaving nearly everyone involved in suspense about Argentina's next move.

Her only public comments came in an unrelated address to the nation Thursday night, when without mentioning Repsol-YPF by name, she said she was "ready to pay all the prices that must be paid" to keep Argentina growing.

Spanish Vice President Soraya Saenz de Santamaria said Friday that Spain will respond forcefully if Argentina follows through with the nationalization. Asked for details, the vice president implicitly drew a sharp distinction between Spain's approach and Argentina's tactic of encouraging speculation.

"These measures aren't advertised, they're simply adopted," she said.