On Tuesday, the European Union and the U.S. promised a total of nearly $300 million.
The head of the U.S. delegation, Assistant Secretary of State Anne Richard, lauded the donations from Gulf nations, which often bankroll their own aid efforts but are not traditional top donors to U.N. programs. She noted, however, that the humanitarian funds are to deal only with immediate needs over the coming months.
"It's good for now, but predictions are that it's not going to be over soon," said Richard, who deals with refugee and migration affairs.
While international aid channels are open to refugee camps in places such as Turkey and Jordan, there is far more limited capacity to organize relief efforts inside Syria because of the fighting and obstacles from Assad's regime.
Paris-based Medecins Sans Frontieres, or Doctors Without Borders, said the U.N. and others need to open more routes for aid to reach rebel-held areas, which now receive only a "tiny share" of international humanitarian help.
"The current aid system is unable to address the worsening living conditions facing people who live inside Syria," MSF president, Marie-Pierre Allie, said in a statement.
The Syrian opposition, meanwhile, has been hobbled by divisions and infighting, which in part has discouraged donors from offering more assistance.
In a sign of persisting friction, Syrian opposition leader Moaz al-Khatib came under criticism Wednesday for comments he allegedly made offering to hold direct dialogue with representatives of the Assad regime if the government releases tens of thousands of political prisoners.
The Syrian government said last week that opposition figures would be allowed safe return to Damascus for national dialogue — an offer flatly rejected by most opposition leaders.
The comments by al-Khatib, who heads the Syrian National Coalition umbrella group, were allegedly posted on his Facebook page, but appear to have been taken down later.
Instead, was a posting: "There are those who sit on their couches and say ... do not negotiate. We don't negotiate about the regime remaining, but for its departure at the lowest cost in blood and destruction."
Associated Press writers Dale Gavlak in Amman, Jordan, and Zeina Karam in Beirut contributed to this report.