At a solidarity meeting held in the Lebanese capital, Beirut, on Tuesday, Lebanese, Palestinian, Jordanian and Moroccan parties and associations issued a statement condemning his detention as well as the bombing of Iraqi churches.
Al-Dhari was detained on Monday in Iraq when a US patrol stopped his motorcade en route to the Association of Muslim Scholars (AMS) headquarters after he had participated in a live TV discussion on the proposed Iraqi national conference.
US forces said they carried out a body scan on al-Dhari and his companions and found TNT traces on his fingers.
Al-Dhari had explained in the televised debate the reasons behind AMS's decision to boycott the conference, listing what he called nine legal violations undermining its preparations and accusing the organisers of fraudulent conduct.
The closure of al-Sadr's paper in
April triggered weeks of unrest
Political parties represented in the interim Iraqi government say the conference will be Iraq's first step towards democracy.
But several Iraqi factions have refused to participate in the conference, saying it is a US-inspired move.
They say no political process can take place under occupation, and that liberating Iraq must be the first priority of all Iraqis.
Together with the al-Sadr movement and the Iraqi Islamic party among other political groups, the AMS has refused to participate in the conference.
Delivering the opening speech of the Beirut meeting, Maan Bashur, chairman of the Pan-Arab Forum, said the arrest was proof of the occupiers' fear of the truth.
"His [al-Dhari's] arrest came after he participated in a live TV talk show. The US occupation is afraid of people like Dr al-Dhari who speak the truth, which the occupation is so keen to hide," Bashur told Aljazeera.net.
Bashur said many of the incidents happening in Iraq are being orchestrated by US and Israel to discredit the "honourable Iraqi resistance".
"Al-Dhari's arrest serves US-Zionist plans. The US occupation is keen to keep Iraqis unaware of who is targeting their infrastructure, civilians and places of worship. Al-Dhari and like-minded people have dedicated themselves to tell the truth, so keeping them free would not be in the interest of US and its allies in Iraq," he said.
Also in the Lebanese capital, the People's Campaign for Support of Iraq and Palestine said it will stage a sit-in on Friday in solidarity with Muthana al-Dhari.
The organisation issued a statement saying its members will call for the immediate release of al-Dhari and Shaikh Mithal al-Harith, an aide to Iraqi Shia Muslim leader Muqtada al-Sadr.
Occupation authorities closed al-Hawza, the newspaper of al-Sadr, last April, triggering an armed rebellion by the Mahdi Army made up of the Shia leader's supporters.