In a phone conversation with Spanish Prime Minister Jose Maria Aznar, Salih said the detention of Alluni was "a political arrest violating the freedom of the press and human rights".
"The president appealed to Mr Aznar to intervene to end this matter, which concerns Arab and Islamic public opinion, as well as those who defend the freedom of the press," official sources said.
A celebrated Aljazeera journalist who earned fame by reporting from the battle fronts of Afghanistan and Iraq, Alluni was arrested in Spain early this month.
Alluni's other career highlights included exclusive interviews with Usama bin Ladin.
Alluni has been charged with links to al-Qaida, a charge that he strongly denies.
Alluni's lawyer has labelled the detention a product of "western bias".
Standing firm by its reporter, Aljazeera has condemned the arrest as an attack on press freedom.