A police officer works inside the operation center at the village of Nea Vyssa near the Greek - Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A police car patrols alongside a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A police officer patrols alongside a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A view of a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A view of a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police drone operator Thanassis Kyriakidis pilots a drone during a patrol at Evros river, near the village of Feres, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officer Dimitris Bistinas operates a long range acoustic device, (LRAD), attached on a police vehicle, during a patrol alongside the Greek - Turkish border near the town of Feres, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A police officer works inside the operation center at the village of Nea Vyssa near the Greek - Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Migrants who were arrested after crossing illegally from Turkey to Greece stand behind a fence at a detention center near the village of Fylakio, at the Greek-Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A view of a steel wall at Evros river, near the village of Poros, at the Greek-Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Migrants who were arrested after crossing illegally from Turkey to Greece stand behind a fence at a detention center near the village of Fylakio, at the Greek-Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officers patrol alongside a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officers patrol alongside a steel wall at Evros river, near the village of Poros, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police drone operator Thanassis Kyriakidis pilots a drone during a patrol at Evros river, near the village of Feres, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officer Dimitris Bistinas operates a long range acoustic device, (LRAD), attached on a police vehicle, during a patrol alongside the Greek - Turkish border near the town of Feres, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officer Dimitris Bistinas operates a long range acoustic device, (LRAD), attached on a police vehicle, during a patrol alongside the Greek - Turkish border near the town of Feres, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

Police officer Dimosthenis Kamargios watches an electronic surveillance tower near the village of Lagyna, at the Greek -Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)

A view of an electronic surveillance tower near the village of Lagyna, at the Greek-Turkish border, Greece, Friday, May 21, 2021. An automated hi-tech surveillance network being built on the Greek-Turkish border aiming at detecting migrants early and deterring them from crossing, with river and land patrols using searchlights and long-range acoustic devices. (AP Photo/Giannis Papanikos)