EU and UN aid chiefs called in Beirut on Saturday for urgent funds to help internally displaced and refugee Syrians, in 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."
Syria has authorised the UN to open eight new field offices to aid the displaced but, "for the first time since the beginning of this conflict, the number of international humanitarian staff inside Syria is decreasing."
"We rely more and more on local staff and on the social fabric of the Syrian society and community organisations that deliver assistance," Georgieva said.
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"But the problem is for this assistance to cross battlefield lines, and that is becoming very, very difficult," she said.
The impact of fighting on the economy has compounded the problems facing those who remain in their country.
"Aleppo used to produce medicines and also chemicals for treatment of drinking water. That production capacity is gone," she said, referring to Syria's former commercial hub and second city.
"Many people are killed or wounded, but on top of it hospitals are destroyed and medical services to the population are gone in many places."
"We just talked to a family who said the price of bread jumped 12 times in the place they came from. In these conditions, unfortunately there is a new strong push that leads to an increase in refugees and that is where our alert has to be high."
For his part, Syria's Muallem told visiting UN Under Secretary General for Humanitarian Affairs Valerie Amos that US and EU sanctions "are responsible for the suffering of Syrian citizens."
He told her the world body "must intervene to ensure (US and EU sanctions) are lifted," according to state news agency SANA.
Muallem also called on the United Nations to "contribute its efforts to rebuild infrastructure and hospitals that were destroyed by armed terrorist groups," a reference to rebels.
Amos said the UN "will continue to provide humanitarian assistance in coordination with the Syrian government," SANA reported.
The United States and European Union have imposed sanctions on Syrian individuals and companies with ties to the regime of President Bashar al-Assad. The EU has also imposed an oil and arms embargo.
A total of more than 43,000 people have been killed since the uprising against Assad's rule erupted in March 2011, according to the Syrian Observatory for Human Rights, which relies on a network of activists and medics on the ground.