Clerics from the two sides of Iraq's religious divide signed a document on Friday declaring that "spilling Muslim blood is forbidden" at the meeting organised by the 57-member Organisation of the Islamic Conference.
The 10-point text, which was drafted by a group of four clerics, draws on verses of the Quran and sayings of the Prophet Muhammad. It calls on Iraqis to safeguard the two communities' holy places, defend the unity of Iraq and urges the release of "all innocent detainees".
The clerics gathered at a royal palace near Makka's Great Mosque to issue their appeal on the last day of prayer of the Muslim holy month of Ramadan.
The document signed by the representatives of the two main branches of Islam stressed the need for Sunnis and Shias to "join ranks with a view to the independence of Iraq and its territorial integrity".
The Organisation of Islamic Conference admitted that the success of its initiative will largely depend on the level of participation by the leaders of the two communities.
A spokesman for the group said the summit was "a meeting of the marjaya [Shia religious authorities] and Sunni ulema [clerics] to anoint the document, which will be distributed to Iraqis and publicised in the media".
The text includes calls to safeguard the "goods, blood and honour of the Muslim", to free innocent people who have been abducted, and "allow displaced people to return to their place of origin".
Shia leader Moqtada al-Sadr, whose Mahdi Army militia seized control of the city of Amara on Friday, did not send a representative to the gathering but gave it his qualified support.
"I support all conferences that go in line with the interest of Iraq, though I would have preferred it to be held in Iraq," he said.
Nuri al-Maliki, the Iraqi prime minister, said he hoped the meeting would give a boost to his government's efforts.
"A conference like that in Makka, whereby Shia and Sunni clerics are to attend, is deemed to be a support to efforts at home to find common ground for dialogue," he said.
None of the participants are considered to among the country's top clerics, but spokesman Salah Abdul-Razaq, speaking to The Associated Press from Mecca, said that the fatwas were vetted and approved by Grand Ayatollah Ali al-Sistani, the country's top Shia cleric.
The challenges facing any attempt to end the violence were underlined shortly after the signing ceremony took place.
A Sunni organsation in Baghdad reported that the son of one of the signatories, Mohsin Abdul-Hamid, had been kidnapped by armed men at a checkpoint in the Baghdad's western Iskan neighbourhood.