Members of the international community are debating their next steps after a U.N. report found evidence that chemical weapons were used in an August attack on a suburb in Damascus.
Colette Fearon, director of Oxfam's program for Syria, said donor countries aren't contributing their share to the humanitarian effort. Oxfam said France, Qatar and Russia are lagging behind other international donors.
"This is not the time for pledges," she said in a statement Thursday. "The situation demands committed funds in order to save lives."
British Prime Minister David Cameron issued a statement through his official Twitter account Thursday saying Oxfam was "right to highlight [the] urgent need" in Syria. Oxfam said Cameron's government has donated more than 150 percent of "its fair share" to the humanitarian crisis.
"While economic times are tough, we are facing the largest man-made humanitarian disaster in two decades and we have to seriously address it," Fearon said.
Oxfam said it supports a political solution to the crisis in Syria.
The U.N. Refugee Agency said Sept. 3 the number of Syrian refugees passed the 2 million mark. That total represents an increase of 1.8 million people since last year.