The two men, Jose Barrionuevo and Rafael Vera, were convicted in July of involvement in the kidnapping of a Basque businessman.

They were denied bail earlier this week pending an appeal.

Thousands voiced their support for Jose Barrionuevo (wearing glasses)

There were emotional scenes outside the prison at Guadalajara north of Madrid as several thousand people gathered to show their support.

Among them was the former Socialist prime minister, Felipe Gonzalez, who is a lawyer and who will represent them at their appeal.

The covert anti-separatist organisation known as Gal is said to have assassinated 28 people they suspected of being ETA members between 1983 and 1987.

It was later discovered that at least a third of them had no connection to the armed group.

Leading socialists linked to violence

Gal's alleged high-ranking connections came to light after statements made by members of the Spanish security services and a determined investigation by journalists.

It was discovered that leading members of the then-socialist government knew about, funded and, it is alleged, organised what amounted to state terrorism.