Mr Poch is said to have been a military pilot during Argentina's conflict
A commercial airline pilot has been arrested in Spain over his alleged role in Argentina's 1976-1983 "Dirty War".
Julio Alberto Poch, a Transavia airline pilot, was held at Valencia airport as he was about to fly a passenger plane to Amsterdam, Spanish officials say.
Mr Poch is wanted in Argentina for allegedly flying planes used to dump political opponents of the country's military regime into the sea.
Some 30,000 people disappeared or died during the junta's rule in Argentina.
'Death flights' pilot
Mr Poch was held during a short stopover at Valencia's Manises airport on Tuesday, Spanish officials said.
DIRTY WAR CONVICTIONS
Ex-President Jorge Videla: Serving a 1985 life sentence for the murder, torture and detention of hundreds
Ex-naval officer Adolfo Scilingo: Given 640 years in prison in 2005 for involvement in death flights
Ex-General Santiago Omar Riveros: convicted in 2009 for murder; his intelligence chief and four others jailed
Ex-police chief Miguel Etchecolatz: serving a 2006 life sentence for kidnap, torture and murder
They said the aircraft of the Dutch Transavia airlines, a subsidiary of Air France-KLM, had been scheduled to be on the ground in Spain for only about 40 minutes.
During this time Spanish police made the arrest after contacting Interpol.
Mr Poch, who has dual Dutch and Argentine nationalities, is said to have been a military pilot at Argentina's notorious Naval Mechanics School - one of the biggest torture and detention centres of the Argentine military regime.
He is alleged to have been involved in the so-called "death flights", in which political prisoners of Argentina's military were drugged and dumped into the sea from the planes.
In 2005, Argentina's Supreme Court struck down amnesty laws which had shielded alleged human rights abusers from prosecution.