The announcement came 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.
The UN humanitarian office said on Tuesday that the number of displaced Syrians has risen from around two million people to 4.25 million.
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The figures -- combined with more than 1.4 million 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 that number to soar to 1.2 million by the end of 2013 -- equivalent to a fifth of the kingdom's population.
According to the Britain-based Syrian Observatory for Human Rights, 82,257 people have been killed in the conflict.
Georgieva told AFP that 60 per cent 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.