EIN EL-HILWEH, Lebanon —

When Syrian warplanes bombed a Palestinian refugee camp in Damascus last December, Umm Sami rounded up her three sons, shut the windows and locked the doors so they could neither hear nor heed the call to arms by rebels and pro-government gunmen fighting in the streets.

Then she told her sons they were leaving their home in the Yarmouk refugee camp in the Syrian capital for neighboring Lebanon, where they would wait out Syria's civil war.

"There will be no more martyrs for Palestine in my family," Umm Sami said, who only gave her nickname for fear of reprisals. "This war is a Syrian problem."

Now safe in Lebanon, the 45-year-old widow and her family have joined thousands of other Palestinian refugees who have found shelter in the country since the uprising against Syrian President Bashar Assad erupted nearly two years ago. The conflict has left more than 2 million people internally displaced, and pushed 650,000 more to seek refuge abroad.

Umm Sami's resolve to keep her sons out of the fight in Syria ties into a deep-rooted sentiment among a generation of Palestinian refugees who say they are fed up with being dragged into the region's conflicts on a promise of getting their own state.

The Palestinian exodus from Syria has also revived a decades-old debate over the refugees' right of return to their homes that are now in Israel. That has added another layer of complexity to a conflict already loaded with sectarian and ethnic overtones that have spilled over into neighboring countries, raising fears of a regional war.

Palestinians living in Arab countries — including the half-million refugees in Syria — are descendants of the hundreds of thousands who fled or were driven from their homes in the war that followed Israel's creation in 1948. Having scattered across the Middle East since then, Palestinians consistently have found themselves in the middle of the region's conflicts.

After the 2003 U.S.-led invasion of Iraq toppled Saddam Hussein, hundreds of Palestinians were killed as the Sunni and Shiite militias fought for dominance of the country. Iraq's Shiite majority saw Saddam, who like most Palestinians was a Sunni Muslim, as a patron of the stateless Palestinians, granting them rights the dictator denied his own citizens because they were of the rival sect.

About 1,000 Palestinians fled the 2004-07 sectarian bloodshed in Baghdad, living in a refugee camp near the Syrian border before being resettled in third countries.

During Lebanon's 1975-1990 civil war, Palestinians played a major role, fighting alongside Muslim militiamen against Christian forces.

Umm Sami, who was born in a refugee camp in Lebanon before the war, was twice forced to flee the fighting, most notably in 1982 when her family escaped the Sabra and Chatilla camps during the notorious massacre of Palestinians there by Christian militias.

She would eventually bury her father, two brothers and her husband — all fallen fighters — before leaving for Syria and settling with her four sons in Yarmouk, one of nine Palestinian camps in Syria.

Her youngest son died in a traffic accident while serving in the Palestinian unit of the Syrian army just weeks before the anti-Assad revolt started in March 2011. None of her other sons joined the revolution, she said, because "they don't want to die."

Unlike in Lebanon, where Palestinians are cramped into notoriously lawless camps, banned from all but the most menial professions and barred from owning property, Palestinians in Syria are well integrated and enjoy full citizenship rights, except for the right to vote.

But when the uprising against Assad erupted in the southern province of Daraa in March 2011, some Palestinians living in a camp there joined in the peaceful protests. When the fighting spread to the northern city of Aleppo in last summer, some took up arms against the regime.

In Damascus, most stayed on the sidelines, but as the civil war reached Yarmouk late last year, a densely populated residential area just 8 kilometers (5 miles) from the heart of the capital, most residents backed the rebels. Some groups, however, such as the Popular Front for the Liberation of Palestine-General Command, opted to fight alongside Assad's troops.

Palestinian officials say more than 700 Palestinians have been killed in the Yarmouk fighting. Most of the camp's 150,000 inhabitants have fled, according to the U.N. agency for Palestinian refugees. Some of them have found safe haven in areas of Damascus and other Syrian cities, but most have escaped to camps in Lebanon.

"We go from catastrophe to catastrophe, from refugee camp to refugee camp, but at least we are alive," Umm Sami said in Ein el-Hilweh, Lebanon's largest Palestinian refugee camp, near the southern port city of Sidon. She and her sons, who are all in their 20s and university graduates, fled Yarmouk with only the clothes on their backs, leaving behind a two-bedroom apartment and jobs that paid the bills.

Now, they are jobless in Lebanon, officially barred from legal employment, and left to live off help from relatives and handouts from the camp's mosques.

Ein en-Hilweh normally houses 65,000 people, but since mid-December, when a flood of refugees from Yarmouk started arriving, the population has steadily grown by several hundred a day, putting a further strain on resources.

Palestinian President Mahmoud Abbas said he asked U.N. chief Ban Ki-moon last month to seek Israeli permission to bring Palestinians caught in Syria's civil war to their homeland. Last week, he said that Israel agreed to allow 150,000 Palestinians refugees from Syrian into the West Bank and Gaza — as long as they relinquished the right of return to what is now Israel. Abbas said he refused.

With no end to the Syria conflict in sight, residents of Ein el-Hilweh have started building a camp within a refugee camp for their compatriots escaping the violence across the border.

They've converted the camp's children's library into housing for dozens of families. Reading rooms, offices, hallways and even bathrooms have been partitioned with makeshift walls, boards and even blankets as families try to carve out space to cook, eat and sleep.

In the library's front yard, a new structure is being built to house at least 10 more families.

"We do what we can to help and find them a home, because they are not going back to Syria soon," said Sheik Jamal Khatab, who oversees the registration of refugees and distribution of aid.

The biggest challenge facing the Palestinian refugees, Khatab said, is not to be dragged into the Syrian civil war — on either side. He also warned that the hardship awaiting Palestinians after the war ends will be tougher than the one they have been living as stateless people.

"It's in our interest not to interfere in this conflict, even though the Syrian regime is a tyrannical regime," he said. "We are not Syrians, and any side that will win this war will consider us