Kuwait's emir pledged on Wednesday to give US$300m to help fund humanitarian efforts for millions of Syrians affected by nearly two years of conflict.
Sheikh Sabah al-Ahmad al-Sabah told a meeting targeting potential donors that "horrifying reports" of violence had raised questions over the future of Syria and aid efforts had to be redoubled.
Wednesday's conference will seek pledges of US$1bn of aid for Syria's neighbours, who are sheltering 700,000 registered refugees, and another US$500m to bankroll humanitarian work for 4m Syrians inside the country.
The aid would fund operations for the first half of this year, but the United Nations has so far received pledges covering just 18 percent of the target, unveiled last month as the scale of Syria's humanitarian crisis escalated sharply.
"We have every reason to be optimistic that there will a very good presence and new pledges that will be coming up at this conference," Robert Watkins, UN humanitarian coordinator in Lebanon, told Reuters.
Lebanon has seen the biggest influx of refugees from the Syrian bloodshed.
US President Barack Obama has announced an additional US$155m in humanitarian aid for Syria, bringing the total US contribution to some US$365m, the State Department said.