The Brussels-based rights organization, Equipo Nizkor, names the suspects as John Demjanjuk, a retired, 88-year-old auto worker in Ohio who is also being sought by Germany; Anton Tittjung; Josias Kumpf; and Johann Leprich.

All four face deportation from the United States but no country is willing to take them in, the group said.

The group said it is acting under Spain's principle of universal jurisdiction. This states that war crimes, crimes against humanity, terrorism, torture and other heinous offenses can be prosecuted in Spain even if they are alleged to have been committed abroad.

Spanish judges have used the principle to go after the late Chilean dictator Augusto Pinochet, al-Qaida leader Osama bin Laden and figures from Argentina's so-called "dirty war" of the 1970s and 80s, among other people.