Authorities in Istanbul set a four-week deadline on Monday for Syrians living without approval in Turkey's largest city to return to provinces where they are registered or face forced removal to those regions.

It was not immediately clear how many people could be affected by the order, but Istanbul's new mayor has said that a total of 1 million Syrians live in the city compared with Interior Ministry figures showing 500,000 are registered.

Turkey's recession-hit economy and high levels of unemployment have fueled anger against the 3.6 million Syrians living in Turkey, the largest refugee population to have fled the eight-year-old civil war in neighboring Syria.