"Since the start of the war, our citizens have been able to cross into Iran without restriction, however Iran has imposed restrictions on its own citizens and is not letting them cross to our side," Interior Minister Mustafa Ciftci told journalists.

He did not say when the exit restrictions began.

Initially, Iranians had been able to cross into Turkey, AFP correspondents at the Kapikoy border crossing said, although they appeared to be few in number.

"Since the start of the war, there has been a fall of a quarter or almost a third in the number of Iranian citizens crossing into Turkey," he said.

At the same time, "there has been an increase in the number of Iranian citizens crossing (from Turkey) to their side," he said, without giving numbers of entries and exits.

There are three crossings along the 500-kilometre (300-mile) frontier between Turkey and Iran.

On March 2, both sides had mutually agreed to suspend day-trip crossings.

"We have been closely monitoring our border crossings... and observing the entries and exits since the start of the war," Ciftci said, insisting there were "no problems at the moment".

Turkey has not given any updated figures on border crossings since March 4, when Ciftci said around 2,000 people crossed each way.

Iran's neighbours have long feared that an attack on the country could destabilise the entire region, unleashing a influx of refugees -- which so far has not happened, despite nearly three weeks of US-Israeli air strikes.

Turkey currently hosts more than 74,000 Iranians with residence permits and some 5,000 refugees.