GENEVA - The UN voiced concern on Friday that conditions are so dire in Syria that some Lebanese residents who had fled there seeking refuge from the Israel-Hezbollah war are opting to return to Lebanon.

There are "Lebanese families who are beginning to take the very difficult and potentially life-threatening decision to return to Lebanon", said Gonzalo Vargas Llosa, the United Nations refugee agency's representative in Syria.

"These are very, very small numbers, but for us, even small numbers are worrying signals," he told reporters in Geneva via video link from the Syrian-Lebanese border.

The UNHCR estimates that around 560,000 people have fled into Syria from neighbouring Lebanon since late September, when months of cross-border fire between Israel and Hezbollah over the war in Gaza escalated into all-out war. Lebanese authorities put the number even higher, at more than 610,000.

Mr Vargas Llosa said that around 65 per cent of those crossing into Syria – itself torn apart by 13 years of civil war – were Syrian nationals who had sought refuge in Lebanon from that conflict.

He hailed the "exemplary" and "extraordinary display of generosity" shown towards those arriving by communities across Syria, "whose infrastructure is destroyed, whose economy is destroyed".

But he warned that given Syria's own "catastrophic economic situation... it is unclear for how long this generosity will last". Worrying signs were already emerging, he said, pointing to the small numbers of people who were opting to return to Lebanon despite the risks.