GENEVA (AFP) - The United Nations on Friday launched a record US$5.2 billion (S$6.4 billion) aid appeal to fund operations in Syria and neighbouring nations, saying the number of people affected by the country's brutal conflict was set to spiral.

The sum by far overshadows the US$2.2 billion the UN sought in 2003 to help cope with the crisis sparked by the war in Iraq.

The US$5.2 billion represents money needed across this year to pay for operations that have already been undertaken, are ongoing, or are due to be carried out until the end of December.

"The figure for the new appeal is both an expression of the alarm about the situation facing Syrians and an absence of a political solution," said Mr Adrian Edwards, spokesman for the UN's refugee agency, the UNHCR.

It also marked a more than threefold increase on the US$1.5 billion which the UN previously had said it needed to cover operations this year. The UN has so far received US$1 billion of that sum, after launching an appeal last December.

In the latest appeal, the world body said a total of US$3.8 billion was needed to help Syrian refugees who have spilled across the country's borders to escape fighting in their homeland. The figure for operations inside Syria, meanwhile, was US$1.4 billion.

More than 94,000 people have been killed and some 1.6 million Syrians have fled the country since the civil war began in March 2011 after a crackdown on protests against the regime of President Bashar al-Assad.

"The numbers represented in this plan are staggering," said Mr Amir Abdulla, deputy executive director of the UN's World Food Programme.

"They represent a tragedy for Syria and a burden on the region," he told reporters.

The overwhelming majority of the refugees have fled to neighbouring Lebanon, Turkey, Iraq and Jordan, which are struggling to cope. In Jordan, for example, one refugee camp is now the equivalent of the nation's fifth-largest town.

With the revolt against Mr Assad having morphed into a viciously sectarian conflict, the total number of refugees is expected to swell to at least 3.45 million by the end of this year, according to the UN appeal. Within the country, a total of 6.8 million people are forecast to need aid this year, the majority of them people who have been forced to flee their homes because of the fighting.

"These are huge numbers. They are not sustainable over the very long term, which is why we hope that there will be a solution to the situation inside Syria," said Mr Abdulla.

"We hope that the world will respond, as millions of Syrians displaced in their home country, and refugees in neighbouring countries, basically have little else to rely on at this time," he added.

Syria's pre-war population was 20.8 million.

"By the end of the year, half of the population of Syria will be in need of aid," underlined Mr Edwards.

The nature of the Syrian conflict has affected aid efforts, with convoys often having to clear dozens of checkpoints manned by different militias from both sides.

"In other operations, there's often a front line when you're dealing with two opposing forces. In this instance you've a very complex situation where there are pockets. There is no clear line. You're dealing with a fragmented opposition who don't follow a monolithic command and control structure," said Mr Abdulla.