Bulgaria has for the first time blocked around a hundred migrants from entering through its southern border with Greece, sending a "strong message" to human traffickers, a minister said Sunday.
Among them were 56 Afghans who were found hiding on board a freight train, as well as another group of some 40 Syrians and Iraqis.
Both groups were stopped on Saturday in what was the largest number of people caught trying to enter the eastern European country since the start of the migrant crisis.
"Their return was carried out at a record speed for Europe," said Prime Minister Boyko Borisov after meeting border police and an army unit in the southwestern town of Blagoevgrad.
"We have sent a strong message to traffickers who area exploiting these unfortunates," added Interior Minister Rumyana Bachvarova.
Following the recent evacuation of the squalid Idomeni migrant camp on the Greek-Macedonia border, where thousands had been stranded after Balkan states closed their borders, Bulgaria has been bracing for an influx of people seeking a new route to Europe.
The Afghans were returned to Greece the same day, while the other 40 are being investigated and will likely be sent back in the coming week, Borisov said.
The migrants had each paid traffickers 200 euros per person believing they were being taken into Macedonia, he said.
In order to manage any further incidents, a contingent of 65 soldiers equipped with 4x4 vehicles would be deployed along the western part of the Greek border to back up the border police, he said.
Bulgaria's border with Greece is nearly 500 kilometres (300 miles) long, and it also shares a 260-kilometre (160 mile) frontier with Turkey.
So far, Sofia has concentrated on buttressing its Turkish frontier, speeding up construction of a 132-kilometre (820-mile) fence which is some three metres (10 foot) high.
But earlier this year, Borisov said the Greek frontier was "the major threat", saying if necessary, Sofia would erect a barrier there too.
Situated on the European Union's eastern flank, Bulgaria registered 5,010 asylum seekers this year, among them Syrians, Iraqis and Afghans.