Syria crisis: UN appeals for $1.5bn humanitarian aid
The UN is appealing for $1.5bn (£920m) to fund relief efforts for those affected by the conflict in Syria.
Officials said $1bn was needed to meet the needs of the million people expected to have fled across Syria's borders by mid-2013.
More than 525,000 Syrians have already crossed into neighbouring countries.
The UN is also seeking $500m to provide aid to a further four million people inside Syria, half of whom have been displaced from their homes.
The announcement came as Syrian government forces were reported to be carrying out a broad offensive against rebels in the suburbs of the capital, Damascus.
The official Sana news agency said there had been clashes in the outskirts of Darayya, Harasta, Douma and Hajar al-Aswad.
On Tuesday, warplanes bombed the Yarmouk Palestinian refugee camp for the second time in a week, sending thousands fleeing. Rebels have been fighting a pro-government Palestinian group for control.
'Truly desperate condition'
Launching the appeal in Geneva, Radhouane Nouicer, the UN's regional humanitarian co-ordinator, said the magnitude of the crisis in Syria was "indisputable".
"The violence in Syria is raging across the country," he added. "There are really no more safe areas where people can flee."
The UN High Commissioner for Refugees (UNHCR) said its request for $1bn was based on planning estimates that up to a million refugees would need help in neighbouring countries during the first half of 2013.
Some 525,000 have so far either registered with the UN as refugees or are being assisted, a seven-fold increase since May. Many more are in Turkey, Lebanon, Jordan, Iraq and Egypt, but have not yet registered.
Between 2,000 and 3,000 refugees are arriving every day.
"Unless these funds come quickly, we will not be able to fully respond to the life-saving needs of civilians who flee Syria every hour of the day - many in a truly desperate condition," Panos Moumtzis of the UNHCR said.
"We are constantly shocked by the horrific stories refugees tell us," he added. "Their lives are in turmoil. They have lost their homes and family members. By the time they reach the borders, they are exhausted, traumatised and with little or no resources to rely on."
UN officials said they would need to provide food, shelter, medicines and even schools for them over the next year.
Inside Syria, UN aid agencies said they required $519.6m to help four million people in need of urgent humanitarian assistance, including an estimated two million who had been displaced from their homes by the fighting. They too were in desperate need of food, shelter, water and emergency medical services, they added.
In total, the UN estimates that 25% of Syria's population now need humanitarian relief.
The BBC's Imogen Foulkes in Geneva says the size of the appeal is a clear sign that UN aid agencies expect the situation in Syria, already described as a massive humanitarian crisis, to get even worse.
The UN has received 70% of the $487m it appealed for in September.
Opposition and human rights activists estimate that more than 43,000 people have been killed since the uprising against President Bashar al-Assad began in March 2011.