The US State Department's Kelly Clements said the money will go to the UN World Food Program, which feeds nearly six million Syrians inside and outside the country every month.
"We will continue working through all possible channels to provide aid to those in need wherever they reside," Clements, deputy assistant secretary for the department's bureau of population, refugees and migration, told reporters in Geneva.
Saying the "dire situation facing Syrians requires an urgent collective response," Clements announced the aid as US officials meet over the next two days in Geneva with key donors and the heads of international organisations responding to the Syria crisis.
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The meetings, she said, will provide an opportunity to discuss not only the problems in Syria but also the humanitarian crisis in Iraq.
Clements said the US will announce additional funding when it joins donors from Europe, the Middle East and elsewhere at a new pledging conference in Kuwait next month.
Since the Syria crisis erupted nearly four years ago, the United States has contributed nearly $1.6 billion for humanitarian aid inside Syria and another $1.5 billion for Syrian refugees in neighbouring countries.
Trouble began in March 2011 with peaceful anti-government protests which spiralled into a civil conflict after a government crackdown, and the violence has killed more than 210,000 people.