DAMASCUS - 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 sum by far overshadows the $2.2 billion (1.7 billion euros) the UN sought 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 the regime of President Bashar al-Assad.

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.

"The figure for the new appeal is both an expression of the alarm about the situation facing Syrians and an absence of a political solution," Edwards said.

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 Hezbollah forces 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 (Syrian) army is seeking to impose its complete control of Qusayr and the surrounding area," Observatory director Rami Abdel Rahman told AFP. "It is leaving no way out for the rebels, and also not for the wounded or for civilians. It wants to annihilate the rebels or take them prisoner." Qusayr's capture gives Assad the upper hand if a US-Russian plan for the first direct peace talks with his opponents materialises, analysts say.

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 Israeli-occupied Golan Heights prompted Austria to say it was withdrawing its peacekeepers 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.

The UN Security Council was to hold talks on the UNDOF crisis later on Friday.

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.

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.