The European Commission announced on Sunday an additional 65 million euros ($84 million) in aid for Syrian refugees and internally displaced, warning the crisis is "already at breaking point".
The announcement was made in a statement released to coincide with a visit to Syrian refugees in Jordan by humanitarian aid commissioner Kristalina Georgieva.
"The more atrocities and fighting go on in Syria, the more people run. There are no indications whatsoever that this ... is going to go down," Georgieva told AFP after visiting the Zaatari refugee camp in Jordan's north.
As temporary home to more than 160,000 Syrians, Zaatari is equivalent to the kingdom's fifth largest city, according to the United Nations.
"We have to dig deep into our pockets (to help the Syrians) because the worst is yet to come. The crisis is beyond humanitarian response. We need to do more and we need do more in a better way," Georgieva said.
The UN humanitarian office said on Tuesday that the number of displaced persons has gone up from around two million people to 4.25 million.
The figures -- combined with more than 1.4 million Syrians who have fled abroad -- mean that more than a quarter of Syria's pre-war population of 22.5 million have been forced to quit their homes since the conflict erupted in March 2011.
In its statement, the commission said it was announcing an additional 65 million euros "in response to the rapidly growing scale of the humanitarian crisis resulting from the conflict in Syria".
"The additional funding will be spent inside Syria, to assist the more than four million people who have been forced to flee their homes, and in neighbouring countries that have generously welcomed some 1.4 million refugees."
Jordan says it is hosting more than 500,000 Syrian refugees and the UNHCR expects the number to soar to 1.2 million by the end of 2013 -- equivalent to a fifth of the kingdom's population.
"Unless all those involved in the fighting as well as the international community find a political solution to the violence very soon the humanitarian community will simply be unable to cope with the unprecedented scale of the needs -- we are already at breaking point," Georgieva warned in the statement.
She told AFP that 60 percent of the refugees are under 18.
"That means a whole generation is at risk of being lost in this conflict. This requires the international community to find ways to help the youth of Syria," she said.