A heavily U.S.-funded refu­gee relief program has begun quietly preparing for a humanitarian crisis on the Iraqi-Syrian border.

The U.N. Refugee Agency in Iraq has amassed hundreds of tents, blankets, plastic sheeting and other supplies just inside Iraq’s western border in case some of the more than 400,000 Iraqis who fled to Syria because of war and sectarian killing need to rush back to escape an escalating conflict in Syria.

Tents and supplies for an additional 30,000 have been stockpiled just across the Iraqi border in Jordan. And the Iraqi government has committed to chartering flights from Damascus to return Iraqi refugees en masse should the Syrian situation deteriorate rapidly.

“If the regional unrest reached Syria, which it now has, we wanted to be ready for a large-scale return of Iraqi refugees,” said Brian C. Vaughan, who coordinates the Iraq effort for the agency, formally known as the U.N. High Commissioner for Refugees. “If it goes beyond instability into armed conflict, then we might anticipate Syrians actually coming into Iraq . . . or fleeing to the north, east or south, too.”

In the past week, the back-and-forth flow of traffic over the desert berm that separates Iraq and Syria has tilted toward Iraq with a net of nearly 1,500 refugees returning at least temporarily, according to UNHCR. But several have arrived packing as if they have no plans to return anytime soon. TVs, washing machines and other household items are increasingly common sights on buses and in convoys of loaded down sport-utility vehicles arriving from Damascus.

More than half of the returning Iraqis from there say they are concerned about their security, according to polling conducted by UNHCR workers at border crossings in the past two weeks. Most of the Iraqi refugees are Sunni Muslims, and the Syrian government is dominated by the Alawite sect of Islam.

“The majority of people are telling us they are not happy with the security situation there, so we’re going to come back [to Iraq] for a little while, but the hope is to go back to Syria,” Vaughan said. “Nonetheless, they’re saying they probably would not have undertaken this trip if they had not been feeling insecure in Syria, given the unrest.”

Some refugees returning to Iraq this week said they increasingly feel targeted and caught between two unpredictable forces. Some had broken bones and wounds that they said came from beatings by Syrian security forces.

But returnees also express apprehension about the security situation in Iraq, saying they are not certain they’ll find a safer situation where their journey ended than where it began.

“We just came back to see,” said Lika Abbas, who arrived on a bus this week just after sunrise. Lugging a large green cooler stuffed with food and her three children in tow, ages 5, 12 and 16, Abbas quickly loaded a taxi and set off for a relative’s home across Baghdad. “We will visit family and then go back in a couple of weeks — I hope.”

For Abbas and others contemplating a permanent return, the challenges that remain in Iraq are laid bare in the first stiff-legged steps following the all-night bus ride.

The once-bustling bus stop along al-Lekaq Square in northern Baghdad remains less a gathering spot than a gridlocked maze of razor wire and barricades. For safety, passengers are dropped off out of view of passing traffic, behind a concrete wall pock-marked with bullet holes and mounds of trash and debris.

Among returning Iraqi refugees who were interviewed Thursday, Haitham Ibrahim, 44, said his family was fleeing the Syrian city of Homs because they “could not stand the situation anymore.”

“The Syrian revolutionaries, they don’t want us to stay anymore,” Ibrahim said. “They accuse us of being part of Bashar al-Assad’s regime. And the Syrian forces, they have started to arrest some of the Iraqis and accuse them of being part of the demonstrations. We had to leave.”

Saeed Kaml, 49, had a bruised nose he said was broken during a three-day detention by Syrian police. He said he was arrested after he inadvertently got too close to a protest in a province south of Damascus.

“The problem is Yemen, Egypt, Libya, those countries that always accepted Iraqis, now the situation there is no good,” Kaml said. “The rest of the Arab countries have closed their borders in our faces. We couldn’t find any other country but Iraq to return to.”

“You see we are back, and we feel sorry,” he added, turning toward his daughters. “This is a wild, militarized country, and now what? My children have stopped their education, and we have sold all our belongings.

Special correspondents Asaad Majeed and Othman Mukhtar contributed to this report.