The UN said Lebanon was struggling to keep pace with the Syrian crisis, with refugees now amounting to almost a quarter of the local population.

"The influx of a million refugees would be massive in any country. For Lebanon, a small nation beset by internal difficulties, the impact is staggering," said UN High Commissioner for Refugees António Guterres.

"The Lebanese people have shown striking generosity, but are struggling to cope. Lebanon hosts the highest concentration of refugees in recent history. We cannot let it shoulder this burden alone."