The beefed up border measures in Turkey, which already hosts nearly 4 million Syrian refugees and is a staging post for many migrants trying to reach Europe, began as the Taliban started advancing in Afghanistan and took over Kabul last week.

Authorities plan to add another 64 km by the end of the year to a border wall started in 2017. Ditches, wire and security patrols around the clock will cover the rest of the 560 km frontier.

"We want to show the whole world that our borders are unpassable," Mehmet Emin Bilmez, governor of the eastern border province of Van, told Reuters at the weekend. "Our biggest hope is that there is no migrant wave from Afghanistan."

Turkey is not the only country putting up barriers: Its neighbor Greece has just completed a 40-km fence and surveillance system to keep out migrants who still manage to enter Turkey and try to reach the European Union.