* Number of vulnerable set to soar as winter bites
* At least 98,000 Syrians out of reach in north
* More than 400,000 Syrian refugees now in region
By Stephanie Nebehay
GENEVA, Nov 9 (Reuters) - An estimated four million people inside Syria will need humanitarian aid by early next year when the country is in the grip of winter, up from 2.5 million now whose needs the world is not fully meeting, a senior U.N. aid official said on Friday.
John Ging, director of operations at the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), said the bleak situation facing civilians caught up in an intensifying civil war between Syrian government forces and rebels was likely to get worse.
"That number in need is going then to increase to approximately 4 million by the early new year. We are not able to scale up at that rate. Since this crisis has begun we have not been able to keep pace with the increasing need," Ging told a news briefing after chairing the Syrian Humanitarian Forum.
"Every day our humanitarian colleagues on the ground are engaging with people who are ever more desperate, ever more fearful for their lives and for the lives of their families because of this conflict," he said.
At least 98,000 Syrians remain out of reach of U.N. agencies, mainly in opposition-held areas in the north near Turkey, though some receive aid from Ankara, Ging said.
The U.N.'s World Food Programme (WFP) is currently distributing enough food for 1.5 million people inside Syria, most of them displaced and living in over-crowded shelters including schools.
But as winter kicks in and basic supplies dwindle the number of vulnerable Syrian families is expected to soar.
"Countless homes, clinics, hospitals and other essential services and infrastructure such as water and sanitation networks have been destroyed or severely damaged," the OCHA said in a document issued at the closed-door talks in Geneva, the sixth such session.
Radhouane Nouicer, U.N. regional humanitarian coordinator, said that the government of President Bashar al-Assad was cooperating and that visa requests for aid workers had not been held up.
"We heard from the government loud and clear last week that the U.N. can go anywhere they want, including to the areas under the control of the opposition. But they will tell us we take you up to the border of this area and then you have to make your way because they cannot enter, otherwise it would be a renewal of hostilities," he told reporters.
More than 400,000 Syrian refugees have already crossed into four neighbouring countries, though far more who have fled have not registered, the U.N. refugee agency UNHCR said.
With 11,000 crossing in the past day alone - into Turkey, Lebanon and Jordan - the overall number is on track to reach 700,000 by early 2013, in line with the UNHCR's forecast issued in late September, officials said.
"The arrival in the last 24 hours is one of the highest in quite some time," said Panos Moumtzis, UNHCR regional coordinator. "The number crossing the border has a direct correlation with the level of security and insecurity inside Syria."
Half the refugees are women and children, many traumatised by the bombing and violence they have witnessed.
"They tell us of increased violence, feeling their lives are under threat and having no other choice but to flee with no other clothes but what they are wearing," Moumtzis said.
A medical aid group, the Union of Syrian Medical Relief Organizations, said on Wednesday Syrian troops were seizing foreign aid and reselling it or channelling it towards government loyalists, putting millions of lives at risk.
Lauren Landis of the WFP said that distribution of aid was monitored and that any suspected diversion was investigated.