In an open letter addressed to the Iraqi people and posted on the internet on Saturday, 26 Saudi scholars and religious preachers stressed that armed attacks launched by Iraqi groups on US troops and their allies in Iraq were legitimate resistance.
The statement came as US troops, backed by air and artillery power, were gearing up for a major assault on Falluja.
The scholars - some of whom have been criticised in the past for their views - issued a fatwa, or religious edict, prohibiting Iraqis from offering any support for military operations carried out by US forces against anti-US fighter strongholds.
"Fighting the occupiers is a duty for all those who are able. It is a jihad (holy war) to push back the assailants," said the letter dated 5 November.
"Resistance is a legitimate right. A Muslim must not inflict harm on any resistance man or inform about them. Instead, they should be supported and protected," it said.
Among the scholars who signed the letter are influential Sunni Muslim clerics Shaikh Safar al-Hawali, Shaikh Nasir al-Umar, Shaikh Salman al-Awda, Shaikh Sharif Hatim al-Auni and Shaikh Awad al-Qarni.
Al-Hawali - jailed in the 1990s for five years without trial because of his criticism of US involvement in the 1991 Gulf war - is known for his radical views and was once close to Usama bin Ladin.
Like many Islamic activists, al-Hawali also opposed the presence of US troops in Saudi Arabia. His name appeared this month on a list issued by a group of Arab intellectuals who seek prosecution of prominent clerics for encouraging what they say is terrorism.
Riyadh has launched a campaign
against anti-government fighters
The religious scholars said their appeal was prompted by "the extraordinary situation through which the Iraqis are passing which calls for unity and exchange of views".
Stressing the need for national unity, the scholars said inter-Iraqi fighting would cause "great damage to the Iraqis and give a free service to the Jews who are infiltrating into Iraq and to the coalition forces which exploit differences to consolidate their domination".
Muslims must be spared
The scholars also urged Iraqis fighting US-led forces in Iraq to spare the lives of Iraqi Muslims and not to target citizens of countries that refused to join the US-led forces that invaded Iraq last year.
The invasion angered many in Saudi Arabia, the birthplace of Islam and home to its two holiest cities.
'Resistance is a legitimate right'
Open letter from Saudi scholars
The Saudi government has launched a military campaign against anti-government fighters that started after al-Qaida-affiliated operatives attacked three residential compounds in Riyadh in May 2003. Several more attacks followed and a number of Westerners have been killed.
The government also began an anti-extremism campaign, reining in clerics who espoused radical views.