EU and UN aid chiefs called in Beirut on Saturday for urgent funds to help internally displaced and refugee Syrians, foreseeing a new phase of a "brutal conflict" that has killed tens of thousands and affected hundreds of thousands more.

In Damascus, meanwhile, Foreign Minister Walid Muallem called on the United Nations to push for an end to Western sanctions, which he said were causing suffering among the Syria people.

UN High Commissioner for Refugees Antonio Guterres told reporters in Beirut that "this is not a conflict like many others. This indeed became a brutal conflict in the context of dramatic humanitarian tragedy."

He called on the world to step up financial support for countries hosting Syrian refugees, saying they require "massive support."

The UNHCR says the number of refugees in neighbouring Lebanon, Turkey, Jordan and Iraq has now reached more than 500,000, and is projected to jump to 1.1 million by June.

EU Commissioner for Humanitarian Aid Kristalina Georgieva said her agency is trying to provide assistance to Syrians inside their country "so they don't need to flee to neighbouring countries.

But that "is becoming increasingly difficult, and in some parts of the country impossible," she added.

The two officials spent Saturday morning in Lebanon's eastern Bekaa Valley, visiting refugees, a third of whom are hosted by Lebanese families, according to the UN.

"While all the refugees we talked to prefer to stay in their home country, they are reporting atrocities and fighting of a magnitude that pushes them out," said Georgieva, adding that "unfortunately the conflict has entered a new phase."