The warning came as the UN launched the largest emergency appeal in history to cope with impact of the civil war.
Heavy fighting continued on numerous fronts yesterday, with rebels attacking an air base in northern Syria and forces loyal to president Bashar al-Assad seeking to capitalise on their own recent gains.
Clashes also continued on the Golan Heights, close to the ceasefire line between Israel and Syria, a day after rebels briefly seized the only crossing between the two foes.
“Syria as a civilisation is unravelling,” said UN High Commissioner for Refugees Antonio Guterres, announcing the appeal for donations worth $5 billion (£3.2bn) by the end of 2013.
Highlighting the scale of the crisis, UN humanitarian agencies in Geneva said 10.25 million Syrians would need aid this year.
“The funds we are appealing for are a matter of survival for suffering Syrians and they are existential for the neighbouring countries hosting refugees,” said Mr Guterres.
Judging by current refugee flows, the UN also forecasts that the Syrian refugee population will double in seven months to 3.45 million from 1.6 million.
Refugees are housed in often squalid camps across Lebanon, Jordan, Turkey, Iraq and Egypt. Lebanese media reported this week that Lebanon might seek to halt the flow, worried that the Syrian war will ignite sectarian hatred at home.
The Lebanese Shiite group Hezbollah has poured men into Syria to help Assad battle the mainly Sunni rebels, playing a crucial role in the capture earlier this week of Qusair – a town on a key route linking the capital Damascus to the coast.
Syrian forces moved yesterday to flush out remaining pockets of resistance around the town. Mr Assad’s army and Hezbollah fighters are expected to turn their attention in the days ahead to rebel positions around the northern city of Aleppo.
Activists said there was heavy fighting in orchards surrounding Qusair and town of Husseiniya. They said that there were many bodies in the fields, including some women and children, adding it was impossible to collect the corpses.
Seeking to regain lost momentum, rebels said they were close to capturing Minagh air base in northern Aleppo province, near the Turkish border.
“There has been a significant advance by the rebels today despite incredibly violent shelling by the regime forces,” said Rami Abdelrahman, head of the UK-based, pro-opposition Syrian Observatory for Human Rights.
“We still cannot say if or when the rebels can take the whole base, but they have made a major push.”
The Syrian war has left at least 80,000 dead and has worsened sectarian divisions across the Middle East. Several leading Sunni mullahs denounced on Friday the participation of Shiite Hezbollah, an ally of Iran.
Hezbollah was founded to fight Israel and had support in the Gaza Strip, a Palestinian enclave ruled by the Sunni-led Hamas group. Gaza preacher Imad Al-Daya, who is not from Hamas, called Hezbollah chief Hassan Nasrallah the “quack of resistance” and urged Sunnis to “wake up this war of religion”.
European Union nations yesterday vowed to ensure the 600 or so EU citizens fighting in Syria were tracked on their return home, fearing they might import al-Qaeda inspired terrorism.