In a statement issued on Tuesday, the Syrian and Jordanian Union of Journalists condemned the arrest of Syrian-born Taysir Alluni last week, famous for his interview with Usama bin Ladin shortly after 11 September 2001.
"To arrest a journalist for performing his duty is a confiscation of the freedom of expression guaranteed by all international pacts," Syria's Union said.
"Targeting journalists with arrest for their professional activities and their search for the truth has become a phenomenon that contradicts human rights and international covenants," the Jordanian Press Association said in a statement.
Alluni himself denies any link to al-Qaida or the Taliban.
But Spanish judge Baltasar Garzon on Monday, ordered the Spanish national be held for an additional 72 hours, until police could provide some evidence to back their claims he provided information and living expenses to al-Qaida operatives.
Garzon is also investigating Alluni's connections with Imad al-Din Barakat Yarkas who was arrested on suspicion of being the ringleader of an Islamist cell, which Spanish authorities dismantled in November 2001.
Spanish state prosecutor Pedro Rubira accused Alluni of involvement in "the organisation of, support for and infrastructure of this cell," according to the warrant for his arrest.
Baltasar Garzon is questioning
Alluni at the high court
Spanish law allows police to detain suspects for three days without access to lawyers or family, with prolonged detention needing judicial authorisation.
Alluni is also accused of "furnishing al-Qaida with funds in Afghanistan," where he was an Aljazeera correspondent during the 2001 US-led war, which brought the end of Taliban rule.
Aljazeera spokesperson Jihad Ballout criticised Spain's detention of Alluni saying it "is another inconvenience to which journalists in general and those from Aljazeera in particular fall victim".
Ballout added that Aljazeera had appointed a lawyer for Alluni and had been in contact with Spanish authorities as well as non-governmental organisations defending the freedom of the press.
Alluni rose to prominence during the Afghanistan and Iraq wars.
Escape from death
He narrowly escaped death when US warplanes bombed the Kabul offices of Aljazeera during the closing days of the war to oust the Taliban in November 2001, when Afghan officials advised him to leave the building.
Alluni was one of Aljazeera's eight correspondents in Iraq, but was expelled by Iraqi authorities during the war. Before that he worked as a translator during the 1990s for Spain's EFE news agency.
Spanish authorities have tracked his movements since at least October 2001, when the newspaper El Pais reported that Alluni's phone had been tapped by authorities while he was working for the agency's Arabic section.