The United Nations launched a record $5.2-billion aid appeal for Syria on Friday as regime forces sought to capitalise on recent victories over the rebels, sending reinforcements to battlefields Homs and Aleppo.
The world body, meanwhile, scrambled to find replacement troops for its peacekeeping mission on the Golan Heights after heavy fighting between regime forces and rebels near its headquarters on Thursday prompted Austria to announce it was pulling out.
The sum sought by the UN by far overshadows the $2.2 billion (1.7 billion euros) that it appealed for in 2003 to help cope with the crisis sparked by the war in Iraq.
But UN officials said the number of people in need inside Syria and in neighbouring countries was set to spiral as the conflict drags on for a third year.
The world body said that a total of $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 $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 President Bashar al-Assad's regime.
The number of refugees is expected to reach 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.
"By the end of the year, half of the population of Syria will be in need of aid," said Adrian Edwards, spokesman for the UN's refugee agency.
Syria's pre-war population was 20.8 million.
Syrian government forces were trying to mop up final pockets of rebel resistance north of Qusayr, the border town which they retook on Wednesday bolstered by Lebanese Hezbollah fighters.
The Syrian Observatory for Human Rights said Assad's forces were also sending reinforcements to Aleppo province in the north, where large swathes of territory have been in rebel hands for months.
"Clashes broke out at dawn between the army and rebels on the outskirts of Dabaa village" north of Qusayr, said the Britain-based group, adding forces of Lebanon's Hezbollah were involved.
The Lebanese army warned of a "plot" to embroil the country in the 26-month conflict, as deadly clashes between supporters and opponents of the Assad regime multiply on its territory.
The Observatory said government forces were also massing "in their thousands" in Aleppo province, aiming primarily to take territory along the border with Turkey.
"They want to cut rebel supply lines from Turkey."
The army's preparations for a new offensive came a day after a brief rebel seizure of the Quneitra crossing on the armistice line separating Israeli and Syrian troops on the Golan prompted Austria to announce to it was withdrawing from the UN Disengagement Observer Force.
UNDOF peacekeepers from the Philippines and India were wounded by mortar shrapnel in fighting for the strategic crossing, according to UN diplomats.
Manila said it too was considering pulling out its 341-strong contingent.
UN leaders held emergency talks late Thursday to replace the 377 Austrian troops who make up more than a third of UNDOF, which has monitored a ceasefire between Israel and Syria since 1974.
President Vladimir Putin proposed that Russian peacekeepers replace the departing Austrian troops ahead of a meeting of the UN Security Council on the UNDOF crisis on Friday.
"Considering the difficult situation that is developing today in the Golan Heights, we could replace the departing Austrian contingent in this region separating Israeli forces from the Syrian army," Russian news agencies quoted Putin as saying.
The Kremlin chief stressed that this was only a proposal and that a formal request had to come from the United Nations and be agreed with both Israel and Syria.
Any deployment of Russian troops would be deeply unpopular with the Syrian rebels who have been angered by Moscow's steadfast support for its ally Damascus with both arms deliveries and political support at the United Nations.
The Observatory, meanwhile, said "fierce fighting continues in Quneitra, including bombardment by regime forces."
Meanwhile, two journalists working for a French radio channel have gone missing in Syria, with no word from them in 24 hours, their employer Europe 1 said.
They were named as Didier Francois, a seasoned reporter in trouble spots, and photographer Edouard Elias, the radio station said.
French President Francois Hollande called on Friday for the two "to be freed immediately".
Since the start of the uprising at least 24 journalists, including several foreigners, have been killed in Syria, according to Reporters Without Borders watchdog group.