Donors have gathered in Kuwait to raise money for 13 million Syrians affected by the war after the United Nations made a record appeal for $6.5bn.
Kuwait's Emir Sheikh Sabah al-Ahmed al-Sabah opened the conference with a $500m pledge and the US promised $380m, but warned that international efforts to ease the suffering of Syrians will fail if President Bashar al-Assad refused to let humanitarian assistance reach the people who need it.
The US is the largest single international donor to the Syrian crisis.
Delegates from 69 nations and 24 international organisations are scheduled to attend Wednesday's summit, chaired by the UN secretary-general, Ban Ki-moon.
At the first donors' conference in Kuwait last January, participating nations pledged $1.5bn, 75 percent of which was delivered, according to a Kuwaiti official.
But Britain's former prime minister, Gordon Brown, who is the UN's envoy for education, said the schooling of Syria's children was as important as delivering food and medicine to refugees.
He told Al Jazeera about a UN plan to educate 400,000 Syrian children.
|Refugee, 14, marries to pay the rent.
"There are children on the streets, there are children begging, in child labour, turning to violence," said Brown.
"Unless we do something about this we have got a huge social problem with dislocation in Lebanon and other areas where refugees are based.
"Why should we concentrate on education? Yes it is important to provide shelter, we must provide healthcare and we've got to provide the other means by which people can survive.
"But if you don't give children education, they lose hope. They can't plan for the future. They can't think of jobs that they may do when the conflict is over.
"We end up with a generation that has lost hope for the future."
Thirteen million reasons
The UN is looking for $2.3bn to support 9.3 million people inside Syria and $4.2bn for Syrian refugees, expected to nearly double to 4.1 million by the end of 2014.
Non-government charity organisations meeting in Kuwait on Tuesday pledged $400m for Syrians, with Kuwait promising $142m of the total.
Rights and aid groups said this week that urgent funds were needed.
"The continuing violence in Syria has sparked one of the biggest humanitarian crises in recent history," Amnesty International said in a statement on Tuesday.
"The world's response to the Syria crisis so far has been woefully inadequate," the group said, ahead of the Second International Humanitarian Pledging Conference for Syria.
Amnesty said the world community must act to end the suffering of Syrian civilians and called on the Syrian government to lift blockades on the civilian population in opposition-held towns and areas.
The UN has described the $6.5bn Syria appeal as the largest in its history for a single humanitarian emergency.