ISTANBUL, Feb. 9 (Xinhua) -- Turkish Interior Ministry announced on Friday that it has stopped issuing new permits to Syrian refugees who apply for residing in Istanbul, the most populous city in Turkey.

"The Directorate General of Migration Management is no more accepting new requests for Istanbul, considering the population density of the city," the Hurriyet daily quoted the ministry as saying in a statement.

Istanbul, the most popular destination for Syrians fleeing a civil war, is hosting more than 542,000 of them.

The figure could have doubled if unregistered refugees were included, said a representative of an non-government organization.

"The authorities apparently decided to combat and curb the influx of Syrian refugees to Istanbul, because there is a massive demand for the city," Veysel Ayhan, the head of the International Middle East Peace Research Center, told Xinhua.

For Ayhan and his aid group, the main problem is the undocumented immigrants who are either already in the city or arriving in the city every day.

"It is not clear how the authorities will cope with these unregistered people," he noted.

During the past one and a half years, security forces have established checkpoints at bus terminals, airports and other transport hubs in Istanbul to stop undocumented Syrians from entering the city.

Despite the fact that undocumented refugees cannot benefit from education and health services, they still prefer Istanbul to other places, Ayhan said.

It seems that the decision by the Interior Ministry also aims to ease the growing discomfort among the public toward the increasing number of Syrians in the country, said Metin Corabatir, the head of the Asylum and Migration Research Center.

"The Syrian refugees have now become more visible not only in Istanbul but across the country, causing more strain between the two communities," he said on the CNNTurk channel.

Turkey is home to about 3.5 million displaced Syrians, but it is "not in a position" to continue hosting them indefinitely, President Recep Tayyip Erdogan said a day earlier.