"I appeal to all sides, and particularly the Syrian government, to stop the killing. In the name of humanity: Stop the violence."
The conference aims to raise $1.5 billion to address a humanitarian crisis that is spinning out of control. Ban noted at the conference that more than 700,000 Syrians have fled the country and roughly 10 percent of the population has become internally displaced.
Shortly after the session got under way, the United Arab Emirates, Saudi Arabia and conference host Kuwait each pledged $300 million in aid.
President Obama, who has been under political pressure to do more to stem the violence, announced Tuesday that the United States would provide $155 million in new humanitarian assistance to Syrians, nearly doubling the American commitment. Obama said the assistance would go toward providing medicine, food, and clothing and blankets as winter approaches.
U.N. officials said the United Nations is seeking to provide at least $1.5 billion in relief. Officials warned Monday of increasingly desperate conditions for about four million Syrians inside the war-torn country and about 650,000 in refugee camps outside.
On Tuesday, at least 65 people were found dead in the contested Syrian city of Aleppo, many of them bound and shot execution-style, according to opposition activists.
The killings provided a sobering backdrop to stalled diplomatic efforts to end the fighting.