Oxfam, in a report released on Thursday, said its research revealed that many donor countries are not fulfilling their pledges and urged them to prioritize funding the UN's $5 billion appeal.
France and Qatar, who back the Syrian opposition and foreign-backed militants, and Russia, which supports the legitimate Syrian government, are among the countries most heavily involved in a conflict that in 30 months has killed more than 110,000 people and forced millions to flee their homes.
But Oxfam said all three countries have committed significantly less aid than what would be "fair" given the size of their national income relative to other donor nations.
"Qatar and Russia have both committed just three percent of what would be considered their fair share for the humanitarian effort, while France is struggling to reach half of its fair share (47 percent)," said Oxfam.
The group's statement comes ahead of an international donors meeting in New York, scheduled for next Wednesday.
"Donors must make real commitments at next week's meeting on Syria and ensure that the money is delivered as soon as possible... The situation demands committed funds in order to save lives," it added.
The UN in June launched its biggest ever appeal for donations to fund the humanitarian response to the Syrian war.
"We're seeing people go without food, shelter and water on a daily basis," said Colette Fearon, who heads Oxfam's Syria program.
"The scale of this crisis is unprecedented and some countries must start to show their concerns to the crisis in Syria by putting their hands in their pockets," she added.
The United States gives only "63 percent of its fair share," according to the report.
Syria has been gripped by deadly unrest since 2011. A very large number of the militants operating inside Syria are foreign nationals.
According to reports, the West and its regional allies - especially Qatar, Saudi Arabia, and Turkey - are supporting the militants inside Syria.
NTJ/NJF