Madrid  - A judge at Spain's top anti-terrorism court Tuesday issued an international arrest warrant for Ignacio de Juana Chaos, 53, the best-known gunman of the militant Basque separatist group ETA, who is believed to have moved to Northern Ireland after being released from prison in August.

National Court judge Eloy Velasco ordered prison without bail for de Juana after he failed to show up in court to be questioned on charges of praising terrorism.

The charges were related to a letter praising late ETA leaders which was read out in de Juana's name at a separatist meeting after his release.

De Juana is believed to have spent the past few months in Northern Ireland, from where his Belfast lawyers proposed to the court that he answer questions by videoconference, Spanish media reported.

De Juana's release on August 2 sparked outrage in Spain. The ETA activist had only served 21 years of a sentence of more than 3,000 years for participating in 11 attacks that killed 25 people, and for writing articles favourable to terrorism.

His release was based on provisions in the prison law in force at the time of his conviction.

The ETA member's time in prison was marked by several hunger strikes. In 2007, he 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 government subsequently eased his prison conditions, prompting protest rallies attended by hundreds of thousands of people.

If de Juana is found guilty of praising terrorism, he could be jailed again for up to two years.

ETA, which is listed as a terrorist organization by the European Union and the United States, has killed more than 800 people in its four-decade campaign for an independent Basque country.

ETA's most recent attack injured 33 people with a car bomb in Pamplona on October 30. dpa( )