Controversy was raging in Spain on Saturday after the release from prison of Ignacio de Juana Chaos, 52, the best-known activist of the militant Basque separatist group ETA who only served 21 years in prison after being sentenced to more than 3,000 years.

De Juana was released from the Aranjuez prison south of Madrid, and was received by two attorneys and his wife.

In 1989, de Juana was found guilty of participation in 11 attacks that killed 25 people and sentenced to more than 3,000 years in prison.

The prison law in force at the time of his trial, however, allowed him to serve only 18 years.

He was subsequently given three more years for threats contained in two articles he wrote for a Basque newspaper, a sentence he completed on Saturday.

De Juana's time in prison was marked by several hunger strikes, the most recent of which he observed for more than two weeks until being released.

In 2007, de Juana refrained from food for more than 100 days, which led to him being taken to hospital and force-fed.

Prime Minister Jose Luis Rodriguez Zapatero's Socialist government subsequently attenuated his prison conditions, sparking furious criticism from the conservative opposition.

Hundreds of thousands of people attended a rally against the concessions granted to a man they regarded as a cold-blooded killer and who has never shown remorse for his actions.

The most recent controversy surrounding de Juana has concerned news that once released, he would move into his wife's flat in a San Sebastian neighbourhood where several victims of ETA also lived.

The National Court is investigating whether the flat was acquired legally by de Juana's wife, whom he married in prison in February.

Former police officer de Juana went underground at age 28 and rose to become the leader of ETA's Madrid cell, participating in major bombings in the 1980s.

The government has pledged to keep a close watch on whether de Juana commits any new offences that could lead him back to prison.

The government was responding to criticism by the conservative opposition, which says the gunman should not have been released.

Radical Basque separatists, on the other hand, see de Juana as a heroic figure.

ETA has killed more than 820 people in its four-decade campaign for a sovereign Basque state, four of them after it ended a 14-month ceasefire in June 2007 following the collapse of an attempt at peace talks with the government.