An alleyway in the Bourj al-Barajneh Palestinian refugee camp in Beirut, Lebanon where jumbled electricity and water cables run over cramped streets. (Caroline Anning/CAROLINE ANNING)

Among the half-million refugees who have poured across the border from Syria into Lebanon is a group of people who find themselves doubly displaced.

To date, an estimated 55,000 Palestinians have sought sanctuary in Lebanon from the war in Syria, according to the United Nations, most of them descendants of families displaced by the creation of Israel in 1948.

As refugees in Syria, they lived in camps and lacked citizenship, but they had built lives, established homes, held down jobs and were generally regarded to have the highest standard of living of any of the region’s more than 4 million Palestinian refugees.

Now that they have been uprooted again, they find themselves with nothing in a country whose own history of conflict with Palestinians means they are far from welcome.

Syrian Palestinians “have gone from catastrophe to catastrophe,” said Ahmed Abu Arab, 62, using the Arabic word “nakba,” which Palestinians have adopted to refer to the 1948 exodus.

Broad-shouldered and smartly dressed, he began to weep as he recounted everything his family had lost when it fled, under fire, from northern Syria this year.

“I am thinking of all our family separated, some left in Palestine, some in Syria, us in Lebanon,” he explained, taking drags on a cigarette with shaking hands. “We had no choice but to leave. The area where we lived was bombed, and our house was hit.”

Abu Arab and six members of his family are being hosted by relatives in a small, two- bedroom apartment in the Burj al Barajinah camp, a squalid settlement of flimsily constructed homes on the southern edge of Beirut that bears the scars of battles fought during Lebanon’s own civil war from 1975 to 1990.

About 16,000 people live here, packed into less than half a square mile of urban space in decrepit apartment buildings. Electricity cables crisscross the dark, labyrinthine alleys, where children play and sewage runs openly.

“It is not like Syria here. I had a nice four-bedroom house in Syria, and there the camps all have services, not like this,” Abu Arab said, gesturing to electricity wires haphazardly nailed to the wall of the spartan apartment.

Burj al Barajinah is one of a dozen Palestinian camps in Lebanon, all of whose populations are being swelled daily by arrivals. They converge on the camps because the U.N. High Commissioner for Refugees, the main relief agency responsible for Syrian refugees, does not have a mandate to help Palestinians. But the U.N. Relief and Works Agency (UNRWA), which does, has not received new funding to deal with the influx.

So the newcomers are left to fend for themselves, depending on the largess of relatives and friends who are already poor. People are living 20 to a room with relatives, and host families are struggling to cope, said Samar El-Yassir, Lebanon country director for ANERA, a U.S. charity that works with Palestinian refugees.

“Palestinians here are already the worst off in terms of poverty, infrastructure and basic services than anywhere else in the region, worse even than Gaza,” she said. “So the poor are hosted by the poorest, and it’s causing huge problems.”

In earlier days, Palestinians went back to Syria when they realized how pitiful the conditions were in Lebanon, relief workers say. But as the fighting has intensified, they have been left with little choice but to stay.

Among the most recent arrivals in Burj al Barajinah were the al-Dahwars — five women with their children in tow — who showed up at a small office belonging to the local aid agency Nejmeh, which also helps refugees. They looked shell-shocked and tired.

“We came only with the clothes on our backs, and we had to walk for seven hours,” said one of the women, who was holding a small child in her arms. Their journey began in April, when they were forced to flee their homes in the Ain el-Tal camp in northern Syria after it was overrun by rebels. Preceding the arc of the fighting, they moved to Aleppo, then to the Yarmouk Palestinian camp in Damascus, and then, as fighting there worsened, they made the arduous journey to Beirut.

According to U.N. estimates, up to 65 percent of the 500,000 Palestinians living in Syria have been displaced by the violence, most of them seeking shelter elsewhere inside the country. Overall, more than 1.5 million Syrians have fled the country, and more than 6.5 million have been displaced internally.

Although the number of Palestinians fleeing to Lebanon is relatively small compared with the number of Syrians who have become refugees, their presence here is considered particularly sensitive as sectarian tensions aggravated by the Syrian war rise regionwide. Most of them are Sunnis, and memories are fresh in Lebanon of the role played by the Palestinians in triggering the Lebanese civil war in 1975. Many fear that another influx of Palestinian Sunnis will again disrupt their country’s fragile sectarian balance.

In one indicator of the potential for conflict, Syrian Palestinians in camps in eastern and southern Lebanon burned aid materials donated by the Shiite Hezbollah movement, which has sent fighters to help Syria’s government crush the mostly Sunni rebellion.

The Palestinians themselves are divided, with some factions supporting the Syrian government and others the rebellion, but many in Lebanon are wary of becoming entangled in another conflict, said Filippo Grandi, UNRWA’s commissioner general.

“I think that Palestinians over the decades have learned the price of being involved in other people’s conflicts,” he said.

But, he added, “it is important to remember how politically sensitive the issue of Palestinian refugees is in the region. It is very worrying.”

Liz Sly contributed to this report.