The UN envoy to Syria, Lakhdar Brahimi, tells Channel 4 News it is "desperately urgent" parties work together to end the war but admits he has not spoken directly to President Assad in three months.
Mr Brahimi described the situation in Syria as "extremely bad, and getting worse" in an interview with Channel 4 News.
He said the burgeoning humanitarian catastrophe was spiralling out of control as hundreds of thousands of Syrians flee ongoing fighting between pro and anti-government forces.
And while he praised the international community's generosity in donating $1.5bn to try and help in January, he said this sum would be necessary every six months unless the situation improved.
"I don't think the international community is going to be able to provide $1.5bn every six months for the Syrians. So it is desperately urgent that some real work is done by everybody to get control over the situation inside Syria, and bring this conflict to an end," he said.
Thousands of refugees are fleeing Syria every day, with more than one million already displaced.
Mr Brahimi said the United Nations was not in a position to police security for refugees because it lacks a police force or army. Inside the camps, it is up to the refugees, he said - and outside the camps, security is the responsibility of the host country.
"The UN is not capable of policing and protecting people in the refugee camps because they don't have the means to do that," he said.
There are also concerns about the pressures the flow of refugees are putting on the host nations, including Turkey, Jordan and Lebanon. On Thursday, Turkey was forced to deny that it had deported up to 700 Syrian refugees following unrest at a border camp.
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Mr Brahimi stressed that the key role for the UN and the wider international community at this point in Syria was to attempt to bring parties together to find a way to end the war - something he admitted could be difficult as he himself has not managed to speak to President Bashar al-Assad since December last year.
Further hurdles to dialogue were put in place on Thursday by Russian Foreign Minister Sergey Lavrov, who called into question Mr Brahimi's own mandate over the decision to give the Syrian opposition a seat at the Arab Summit.
Mr Brahimi said negotiation remained key, adding that he did not believe arming the rebels was the way forward.
"Pouring more arms to the opposition would bring more arms to the government and that will not solve the problem...My hope and also my polite criticism to the international community...I think they should be talking to one another with much, much more urgency, perhaps taking some decisions, going to the security council and speaking to the parties and to the region in much more forceful terms than they have until now."
However, he added: "I'm afraid I do not expect miracles any time soon."
One in five Syrians fleeing the country
The humanitarian crisis in Syria has prompted an urgent appeal from the Disasters Emergency Committee, which launched its Syria donation drive last week.
Leading charity figures, many of whom have recently returned from refugee camps in Syria or neighbouring countries, spoke out today on why aid is so critically needed.
"It's not just bombs and bullets. They've lost the basic building blocks of life. It's having a devastating impact," said Andrew Wander of Save The Children, who has just returned from Jordan. He admitted that charities were struggling to keep up with the numbers arriving in camps in desperate need.
The chief executive of World Vision, Justin Byworth, said the scale of the catastrophe was "unimaginable".
He told Channel 4 News the story of one 14-year-old girl, Hibah, who has a hole in her heart and fled last week with her family. Her 6-year-old cousin died during the trip.
"Now she's living with 13 people in a tiny, bare, common room in a place in the Beqaa valley in Lebanon. It's unimaginable. The situation for children particularly we're concerned about."
Nigel Timmins, Oxfam's deputy humanitarian director, said it was important to remember that Syria was a middle-income country, and many of the refugees were professionals who were stunned and ashamed at what had happened to them.
"There's a sense of fear and uncertainty: How long am I going to be a refugee?" he said.
To donate to the DEC Syria appeal, click here or to give £5, text DEC to 70000.
27 March 2013