Updated

At least 22,300 Iraqis who fled to Syria several years ago have streamed home in the past three weeks, United Nations officials in Baghdad said Tuesday, preparing for more refugees fleeing the escalating Syrian civil war.

The returning Iraqis have been joined by some 3,600 Syrians who have crossed into Iraq since July 23, when Baghdad announced it was opening its western borders to refugees. The Syrians are being kept near the border, evoking some complaints.

The influx represents a stark turnaround from the bloody years following the 2003 U.S.-led invasion of Iraq, when waves of refugees fled in the opposite direction.

While Syria's other neighbors have taken in far more refugees, the influx puts added strain on an Iraqi government still struggling to ensure security and provide basic services to its residents.

The U.N. envoy to Iraq, Martin Kobler, welcomed the Iraqi government's efforts to aid the new arrivals, but he said international donors must contribute more money.

"This is a problem. This is a significant increase in the numbers of refugees," he told reporters. "It happens at a time where it is really a burden, because there is a lack of services also in Iraq."

More than 1 million Iraqis fled to Syria to escape widespread sectarian fighting during the worst of violence in their homeland between 2005 and 2007. Syria was hosting as many as 87,000 Iraqi refugees as recently as May, along with other Iraqis who relocated there but were not counted as refugees, according to U.N. estimates.

They began to pour back into Iraq in large numbers after July 17, when Iraq's government urged its citizens to return home immediately to avoid being hurt or killed in the Syria fighting.

On July 23, Iraqi Prime Minister Nouri al-Maliki opened his country's western border to Syrian refugees.

While Kobler praised Baghdad's decision to host the refugees, he urged Iraqi authorities to grant the Syrians greater freedom of movement.

The Syrian refugees, who cross into Iraq near the town of Qaim, are not allowed to travel onward. Most are in and around school buildings where they are sheltering, according to Claire Bourgeois, an Iraq-based representative for the U.N. refugee agency.

Saliha Jawdat, a Syrian mother of three who arrived in Iraq seven days ago, corroborated that account. She said her family decided to leave Syria after the area near their home came under shelling by government forces.

"The services provided to us by the Iraqi authorities are good, but our movements are restricted," she said. "They are preventing us from visiting and staying with our Iraqi relatives in Qaim. We feel the school room is too small for us, and we want to rent a house."

The mayor of Qaim, Farhan Fitkhan Farhan, agreed that the problem needs to be solved. He told The Associated Press that the Syrian refugees are being kept in area schools while a tent camp is set up, with help from the U.N.

He said the number of refugees has slowed since fighting near the border post died down, though he expects "more people to come, as the security situation is deteriorating in Syria."

"Our goal is to move those refugees to the camp or send some to stay with Iraqi relatives, because we know that schools are not meant to be a residential place," he said by phone.

Authorities in Iraq's self-ruled Kurdish region began hosting Syrian Kurds on their territory late last year. More than 9,000 refugees have arrived there, according to the U.N.

More than 200,000 Syrians have fled to neighboring Turkey, Lebanon and Jordan.

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Associated Press writer Sameer N. Yacoub contributed reporting.