BAGHDAD — When he saw the bodies of men and women left rotting in the streets of Damascus, Hassan Hadi knew that the sectarian violence he had fled Iraq to escape years ago had now come to Syria. Despairingly, he left his belongings and fled again, back home.

Hadi is one of at least 12,680 Iraqis who streamed back to their homeland the past month to escape the Syrian civil war. Most of them are Iraqi Shiites, fleeing a reported rash of attacks against their community, apparently by Syrian rebel gunmen.

The attacks reflect the increasingly ugly sectarian nature of Syria's conflict, where an opposition largely based among the country's Sunni majority has risen up against the regime of Syrian President Bashar Assad, which is dominated by members of the Alawite sect, an offshoot of Shiite Islam. The motives for the attacks on Iraqis are unclear. They may be revenge against any Iraqi because the Shiite-led Iraqi government is seen as siding with Assad. They may also be fueled by sectarian hatreds, with resentment of Syria's Alawite leadership flaring into anger at Shiites.

In July alone, 23 Iraqi Shiites have been killed in Syria, some of them beheaded, according to the Washington-based Shiite Rights Watch. In one gruesome case, the U.N. said an Iraqi family of seven was killed at gunpoint in their Damascus apartment.

But going back was wrenching for Hadi, given Iraq's continued violence. "There are still bombings and explosions here, and when we decided to return to Iraq, it was a hard moment — we cried a lot," he said, speaking at his mother's house in Baghdad, where his family is staying until they can find a home.

The exodus of Iraqis back home is a bitter reversal for refugees tossed back and forth by violence. According to U.N. estimates, more than 1 million Iraqis fled to Syria between 2005 and 2008, when their homeland was on the brink of civil war, torn between Shiite militias and Sunni insurgents butchering their rival communities. Those who fled to Syria were a sectarian mix, though the majority were Sunnis.

Over the past few years, Iraqis have been slowly leaving Syria, many returning home as violence in Iraq eased. Fewer than 200,000 Iraqis remain in Syria, according to the office of the Iraqi ambassador in Damascus.

The recent targeting of Iraqis, however, brought a spike in returns. The majority of Iraqis fleeing Syria for home over the past month are Shiites, according to Saif Sabah, a spokesman for the Iraqi Ministry of Displacement and Migration.

According to U.N. and Iraqi officials, most of them fled Damascus, which in July saw its worst fighting yet of the 17- month-old Syrian conflict. For days, rebels took over whole neighborhoods of the Syrian capital, prompting a ferocious assault by government forces. Amid the fighting, it appears rebel fighters targeted Iraqis in the city.

The U.N. refugee agency said Iraqis in the mainly Shiite Damascus suburb of Sayeda Zeinab in particular were fleeing because of increasing violence in general but also "targeted threats" against them. Sayeda Zeinab saw heavy activity by rebel fighters during the Damascus battles.

Hadi and his family lived in Sayeda Zeinab. He said Sunni rebels and gangs went on a rampage in the suburb. He blamed the Free Syrian Army, the loose umbrella group of rebel fighters.

"The gangs of the Free Syrian Army started to spread in the area, killing women and some children as well as men," Hadi said last week. "The bodies were left on the street for two days because no one could evacuate the casualties. My children were hysterical."

"They are spreading sectarian violence in Syria," Hadi said.

His report and other reports of anti-Iraqi violence could not be independently confirmed since Assad's regime has tightly restricted journalists in Syria. The conflict has seen numerous tit-for-tat sectarian slayings among Syrians, including reported massacres by Alawite gunmen in Sunni areas.

A spokesman for the Free Syria Army strongly denied it has participated in or sanctioned the targeting of Shiite civilians.

"The members of the Free Syrian Army have principles and never do such things," Brig. Gen. Anwar Saad-Eddin said. "The security situation has deteriorated nationwide and that anyone holds a weapon can say he's from the Free Syrian Army. We have already arrested some of them."