Spain has issued an arrest warrant for a man currently on trial in Germany for alleged Nazi war crimes.
John Demjanjuk is on trial in Munich over his suspected role in the deaths of more than 28,000 people at Sobibor concentration camp.
That trial began in November 2009, after the United States agreed to deport him. But the proceedings have been delayed because of questions over the health of Demjanjuk, now aged 90.
But after the Munich trial is completed, he could still be extradited to Spain following an arrest warrant issued by a Madrid court charging him with complicity in genocide and crimes against humanity.
The charges, filed by a Spanish civil rights group, are based on what is alleged to have occurred at Flossenburg concentration camp in Germany, where Demjanjuk served after Sobibor.
The court has jurisdiction because the camp had more than 150 Spanish prisoners, 60 of whom did not survive the Holocaust.
The Spanish charges are the latest development in the long-running investigation over Demjanjuk and what he did during the Nazi years.
After the war the Ukrainian-born Demjanjuk emigrated to Ohio and worked as a car mechanic.
But in 1981 he was found guilty of lying on his immigration form by withholding his SS membership, and deported to Israel where the man remembered by survivors as "Ivan the Terrible" was given a death sentence.
A subsequent appeal on the grounds of mistaken identity led to the charges being dropped, but when more paperwork was discovered he was deported to Germany to face trial.
Elan Steinberg, vice president of the American Gathering of Holocaust Survivors And Their Descendents praised “a remarkable and extraordinary development” in the case.
He said: “It's a visible demonstration that the crimes Demjanjuk is charged with touched all of humanity.”