About 2.5 million people caught up in Syria's fighting need aid, the United Nations says, double the number it estimated in June.
The rise was caused by an upsurge in violence over the summer, particularly in the capital Damascus and the country's economic centre Aleppo, UN officials said.
The United Nations also almost doubled its appeal for funds to buy food, medicine, sanitation equipment and other supplies to $347 million. A total of $103 million funding had already come in and the European Commission on Friday pledged further money.
The Syrian Observatory for Human Rights says more than 23,000 people have died in an uprising against Syrian President Bashar al-Assad that has lasted more than 17 months.
Some 200,000 Syrians have fled to neighbouring Turkey, Jordan and Iraq.
President Assad met the new head of the International Committee of the Red Cross (ICRC) in Damascus on Tuesday and promised to allow the agency to expand its humanitarian operations in his country.