The UN and aid groups urged the West to open its borders to Syrian refugees and called for an end to the conflict, which entered its fourth year on Saturday.
UN refugee chief Antonio Guterres, speaking at a press conference attended by numerous organisations, called for "all borders to be open to Syrians and in particular to Syrian children."
"To see Syrian children drowning in the Mediterranean today after fleeing the conflict... is something totally unacceptable," he said.
"Borders need to be open everywhere, visa policies need to be open everywhere, family unification programmes need to exist everywhere.
"This is the solidarity that the Syrian people deserve."
Nearly three million people have fled Syria since the beginning of the conflict in March 2011, and aid groups say 5.5 million children have been affected.
Syria's neighbours, which already struggle to manage their own limited resources, have been forced to absorb the majority of the refugees.
Lebanon, with a population of just four million, has been most affected. It now hosts nearly one million Syrian refugees, and the UN agencies and aid groups called for it to receive more help.
"We should praise the generosity of the Lebanese people," Save the Children CEO Justin Forsyth said, saying the country's refugee burden would be the equivalent of 20-25 million arrivals in Britain.
"I can't imagine 25 million people coming to Britain and the reaction of the British people. I hope it would be as generous."
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The coalition of aid organisations urged the implementation of a February UN Security Council resolution calling for humanitarian access throughout Syria.
Anthony Lake, executive director of UNICEF, said the Syrian government had agreed to open a border crossing with Turkey to allow access to the Kurdish majority city of Qamishli in the northwest.
But the government has been less accommodating in areas that, unlike Qamishli, are under rebel control, and Forsyth said there was no sign yet of the resolution being implemented.
"We have to be honest, the situation in Syria is getting worse, not better, and it hasn't gotten better since the UN resolution was passed," he said.
Guterres called on the international community to step up efforts to end the conflict, which has claimed more than 146,000 lives.
"Tt is clear that there is no military solution to this war. It is clear that nobody is winning; everybody is losing," he said.
"The war would stop now if arms and money would not be provided to both sides."
The aid groups also asked ordinary citizens to continue to "dig deep" and donate to help Syrians.
"There but for the grace of God go all of our children," said Conny Lenneberg of the NGO World Vision.
"Just because it's not happening to us doesn't mean it's not happening."