Syria is in the throes of a revolt against the government of President Bashar al-Assad, whose efforts to crush the uprising by force have driven thousands of civilians from their homes, many of them into Syria's neighbours.
"We are calling for increased humanitarian efforts and cooperation between international and regional organizations in order to deliver urgent humanitarian aid to the Syrian people in Syria and in neighboring countries," said Ekmeleddin İhsanoğlu, head of the 57-member Organisation of Islamic Cooperation (OIC).
"The amount of aid needed for Syria is $500 million," he said at a press briefing at the OIC's head quarters.
Last month the United Nations refugee agency doubled its forecast for the number of refugees who will flee Syria this year to 185,000 and said it would need $193 million to help them - more than twice the amount previously thought.
Saudi Arabia's King Abdullah launched a nationwide fund-raising campaign last week to help the people of Syria, collecting 440 million riyals ($117 million).
The OIC, of which Syria is a member, aims to safeguard the interests of the Muslim world and has collected aid in the past to help its member states. Last year, the group's pledged $350 million in aid to fight famine in Somalia.