UN Secretary General Ban Ki-moon says that half of Syria’s population now “urgently need humanitarian aid”.
He was speaking at a donor conference in Kuwait to raise funds for the worsening humanitarian crisis.
The UN is asking for $6.5bn (£4bn) over the coming year for Syria, its biggest ever request for a single crisis.
Meanwhile, Syria’s deputy foreign minister has said Western intelligence agencies have visited Damascus to discuss combating radical Islamists.
“Half of the total population of Syrian people, nearly 9.3 million individuals, urgently need humanitarian aid,” Mr Ban said.
It is thought that around that many people have been displaced by the war, both within the country and beyond.
So far the following countries have promised money at the Kuwait conference:
- Hosts Kuwait announced a pledge of $500m (£304m)
- The US promised $380m (£231m) in new contributions
- The UK announced an extra £100m ($164m)
The UN says more than 100,000 people have died since the uprising began.’Deliberate obstruction’
Refugee camps outside Syria’s borders are barely coping and reports from some besieged communities inside the country say people are dying from starvation.
Rights groups have accused the Syrian authorities of deliberately withholding aid from some districts.
“Donors should keep in mind that the human cost of this crisis has been increased exponentially by Syria’s policy of deliberately obstructing aid,” Peggy Hicks of Human Rights Watch said.
The organisation quoted local activists as saying that by 5 January, 28 people had died in the Palestinian refugee camp of Yarmouk, only a few kilometres south of central Damascus.
For communities trapped by the fighting in Syria, which big aid agencies cannot reach, what is needed is not so much more money, but an agreement on local ceasefires or humanitarian corridors, the BBC’s diplomatic correspondent Bridget Kendall reports.
But it is by no means clear the fragile peace process supposed to be launched at an international conference in Geneva next week can make that happen, she adds.
The main opposition alliance, the National Coalition, has still not decided whether to take part in the talks, fearing participation could undermine its credibility with the anti-Assad opposition inside Syria.
Correspondents say the growing disarray of the opposition is frustrating the West and bolstering the confidence of the Syrian government.’No alternative’
Meanwhile, Syria’s deputy foreign minister has told the BBC that Western intelligence agencies have visited Damascus for talks on combating radical Islamist groups.
Faisal Mekdad said there was a schism between Western security officials and politicians who are pressing President Bashar al-Assad to step down.
The UK Foreign Office told the BBC it does not comment on intelligence matters.
However, the BBC’s chief international correspondent Lyse Doucet said informed sources had confirmed meetings between Western and Syrian intelligence officials.
The growth of jihadist groups among rebels fighting President Assad has caused international concern.
On Tuesday, French President Francois Hollande told a press conference in Paris that 700 French nationals had joined the ranks of foreigners fighting in Syria.
In a BBC interview, Mr Mekdad said many Western governments had finally understood that there was no alternative to the leadership of President Assad.
Asked if Western intelligence agencies – including British intelligence – had recently visited Damascus, he said: “I will not specify but many of them have visited Damascus, yes.”
Mr Mekdad also said “many” countries were approaching Syria with a view to having their diplomats return to Damascus.
Khaled Saleh, spokesman for the National Coalition, told the BBC that if the reports were true, “it would show a clear contradiction between the words and actions of the (Western-led) Friends of Syria group.”
The Friends of Syria is a group of countries set up to support the Syrian opposition, with 11 states in the region and in the West comprising its “core group”.