The release order was expected to be carried out late on Monday night or early on Tuesday, but has been set back after a series of delays.
Munzir al-Nimri, general-secretary of the International Committee for Defending Taysir Alluni, said Alluni had still not been released from prison due to procedural reasons and the need to complete more paperwork.
"The procedures involve accompanying Alluni, with his hands chained, by Spanish security guards and include signing an order that has not been signed yet. We are still awaiting completion of these procedures," al-Nimri said.
Alluni will then be taken to his home in Granada where he was first arrested in September 2003.
Alluni is to appear before Spanish police every day while awaiting his trial. He is likely to be under house arrest during the course of the trial, Aljazeera has also learned.
Michael Al-Kik, Aljazeera's correspondent in Granada, said the delays were due to security reasons - the Spanish authorities did not want to disclose information in what they perceive to be a top-security case.
Alluni's morale is helping to keep
him alive, the ACHR's chief says
He said once Alluni is under house arrest with a 24-hour guard, he will not be allowed to leave the premises even for medical treatment unless he has permission from the judge.
Syrian-born Alluni, a Spanish citizen, was first arrested in 2003 on suspicion of links with al-Qaida as part of an investigation into suspected Islamist operations in Spain.
He was then released due to chronic back problems and heart ailments but re-arrested in December 2004 when Spanish authorities feared he might be a flight risk.
Alluni's trial, and those of 18 others suspected of ties to al-Qaida, is expected to begin in late March or early April.
"His high morale is keeping him alive"
Haitham al-Mana, spokesperson for Arab Committee for Human Rights
Haitham al-Mana, spokesperson for the the Paris-based Arab Committee for Human Rights, said three factors led to Alluni's release from prison.
"The involvement of the Qatari and Spanish governments; the appeals from Islamic and international organisations; and the International Solidarity Campaign to Free Alluni launched by Aljazeera were instrumental in pressuring the courts to release him."
Al-Mana, who had visited Alluni in a maximum-security prison ward housing members of crime gangs and Basque separatists, said the journalist was in extremely poor health.
"His high morale is keeping him alive," al-Mana said.
In the first reaction to his release to house arrest, Yusuf al-Shuli, deputy head of the Arab Committee for the Defence of Journalists, said the news was gratifiying for all the organisations and individuals who laboured for Alluni's release.
"All of them are very much pleased that Alluni has been freed, even though he will remain under house arrest. But we are sure he will soon be acquitted."
Al-Shuli said the committee's next move would be to cooperate with international and UN organisations in mounting a campaign to point out the flaws in Spain's anti-terrorism legislation.
Wife Fatma al-Zahra called for
continued pressure on Spain
Wife Fatma al-Zahra said late on Monday she was surprised by the Spanish court's decision to release the award-winning journalist.
She also called on all organisations and campaigns in support of her husband to continue pressuring the Spanish government until Alluni's innocence is proven.
"Then we will ask for a formal apology from the [Spanish] government which will ensure Taysir's dignity," she said.
Bin Ladin interview
Al-Zahra had earlier said her husband was arrested under the pretext of misusing his position as a journalist to interview Usama bin Ladin, during which the latter called for a war against the United States and its allies.
His colleagues suggest his achievements may have counted against him.
His incarceration has sparked outrage among Arab human-rights groups, journalists and colleagues, who describe his treatment as an attack on freedom of the press.