The G7 group of leading economies and Gulf states has pledged US$1.8 billion in funding for UN aid agencies helping Syrian refugees.
The commitment came after UN Secretary-General Ban Ki-moon told world leaders at the opening of the General Assembly debate that UN humanitarian agencies were "broke".
"We have agreed to provide together US$1.8 billion for the international aid organisations of the United Nations, especially the UN refugee agency and the World Food Program," German Foreign Minister Frank-Walter Steinmeier told reporters.
The pledge was announced after a meeting of foreign ministers of the G7 - Britain, Canada, France, Germany, Italy, Japan and the United States - with their counterparts from Kuwait, Qatar, Saudi Arabia, the United Arab Emirates and other European ministers.
The United Nations is struggling to help some 60 million people displaced by conflict, the highest number since the end of World War II.
Four million have fled the war in Syria, with hundreds of thousands travelling to Europe to try to rebuild their lives.
The war in Syria and Europe's migration crisis will take centre stage at the United Nations on Wednesday, as world leaders seek to overcome deep divisions over how to address the turmoil.
Russia will chair a Security Council meeting on terrorist threats that is expected to focus on the crisis in Syria.
Ban will separately host a meeting on Europe's migration crisis aimed at agreeing on a global response.