One of five people living in Lebanon are refugees who have fled the conflict in neighbouring Syria, the United Nations High Commissioner for Refugees said Monday.
The UNHCR says there are more than 842,000 Syrian refugees in Lebanon but the actual figure could be even higher, Lebanese authorities believe.
An additional 52,000 Palestinians who were living in Syria have also taken refuge in Lebanon, the UN's refugee agency said.
The UNHCR figures do not include hundreds of thousands of Palestinian refugees who have been living in Lebanon for decades, most of them in insalubrious camps across the country.
One in five residents of Lebanon is a refugee coming from Syria, the UNHCR said, adding: "They live in 1,588 locations."
Lebanese authorities have refused to set up official camps for refugees from Syria. Many live in hundreds of unofficial tent settlements across the country, mainly on Lebanon's northern and eastern peripheries.
Better-off refugees rent apartments in towns and cities, but face exorbitant rents.
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The UNHCR said "30 percent live in substandard shelters" and 72 percent are "in need of continued humanitarian assistance."
The refugee crisis is also impacting Lebanon's population by stretching the country's resources, the agency said, putting the number of Lebanese affected by the influx at 1.2 million.
Of the Syrian refugees, 280,000 are children of school age, only 130,000 children of whom have been provided with education services, the UNHCR said.
Lebanon is hosting the highest number of refugees from Syria, while more than a million others have fled to Jordan and Turkey.
On Monday, the UNHCR said the number of Syrian refugees in the Middle East will nearly double over the next year to exceed four million, putting an enormous strain on neighbouring countries.
The refugee crisis has brought serious economic and political challenges to Lebanon, where there are regular clashes linked to the war in Syria.
Lebanon is sharply divided over the war in Syria, whose regime dominated the small Mediterranean country militarily and politically for 30 years until 2005.