The number of Syrian refugees in Lebanon has surpassed 1 million, the UN refugee agency said yesterday.

It called the figure a “devastating milestone” for the tiny country with only around 4.5 million people of its own.

Three years after Syria’s conflict started, Lebanon has become the country with the highest per capita concentration of refugees recorded anywhere in the world in recent history, the office of the UN high commissioner for refugees said.

As a result, Lebanon is struggling to cope with a massive crisis that has become an unprecedented challenge for aid agencies.

The million Syrians are a huge burden for Lebanon, the office said, adding that it registers 2,500 new Syrian refugees daily in Lebanon — more than one person per minute.

In addition to the registered refugees, there are tens of thousands of other Syrian refugees who are not registered and Lebanese officials estimate their number to be as high as 400,000.

“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 Antonio Guterres.

And his office added that the influx was accelerating.

In April 2012, there were 18,000 registered Syrian refugees in Lebanon, but by April 2013 they reached 356,000 and yesterday they reached the million mark.

The World Bank estimated that the Syria crisis cost Lebanon $2.5 billion (£1.5bn) in lost economic activity during 2013 and now threatens to push 170,000 Lebanese into poverty by the end of this year.