Juan Jesus Narvaez Goñi and Itziar Alberdi Uranga are suspected of belonging to the separatist group Euskadi Ta Askatasuna, or ETA, and had been fugitives for 22 years. They are accused of taking part in several attacks around the time of the 1992 Summer Olympic Games, which were held in Barcelona, Spain.
ETA is believed to have been responsible for hundreds of deaths since taking up arms in the late 1960s to fight for an independent Basque region. The group agreed to a cease-fire in 2011.
The arrests in Puerto Vallarta demonstrate that the Spanish government remains committed to tracking down far-flung members suspected of past crimes.
Since the cease-fire, Spain has arrested other ETA members in Britain, Belgium, Italy, France, Venezuela and Brazil.