Bashar Al Assad's Syria faces suspension today from the representative body of the Muslim world, the biggest international organisation outside the United Nations.
The Organisation of Islamic Cooperation meets in Mecca with the suspension already approved by its executive committee.
The conflict in Syria is a threat to "peace in the entire region" and OIC members must take "decisive and firm measures" to end it, said Prince Turki bin Mohammed bin Saud Al Kabeer, a senior official at the Saudi foreign affairs ministry.
The OIC say they do not know if Syria will attend the summit because invitations are the prerogative of the host, Saudi Arabia.
The Arab League expelled Syria nine months ago, and said Damascus could not rejoin until it removed armoured units from cities, released protesters from detention and started talks with the opposition.
Today's meeting is expected to be stormy. Mahmoud Ahmadinejad, the president of Iran, Mr Assad's closest ally, arrived yesterday for the meeting, which he described as "a historic test for hosts and participants to protect the long-term goals, dignity and essential rights of Muslim nations".
The regional situation is "a bit complicated", he said before he left Tehran. "Enemies use a significant portion of the energy of Muslim governments and groups for eliminating and damaging each other."
Mahdi Alfathallah, the OIC's political director, dismissed concerns that tensions would rock the summit, which will also discuss Myanmar, Mali and the Palestinian situation.
"These countries are not coming to Mecca to dispute between each other," he said. "Everybody is coming to help solve the crises."