Police in Bulgaria on Friday discovered an abandoned truck containing the bodies of 18 migrants, who appeared to have suffocated to death inside a secret compartment under a load of lumber.

The Interior Ministry said that according to initial information, the truck was carrying about 40 migrants and the survivors were taken to nearby hospitals for emergency treatment.

Bulgarian Health Minister Assen Medzhidiev said most of the survivors were in very bad condition.

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"They have suffered from lack of oxygen, their clothes are wet, they are freezing, and obviously haven’t eaten for days," Medzhidiev said.

The truck was found abandoned along a highway near the capital, Sofia. The driver was not there, but police discovered the passengers in a secret compartment below the lumber the vehicle also was carrying.

Authorities did not immediately give the nationalities of the migrants. Bulgarian media reported they all were from Afghanistan.

Bulgaria, a Balkan country of 7 million, is located on a major route for migrants from the Middle East and Afghanistan to Europe. Only a small number of them plan to stay in the European Union’s poorest member, using Bulgaria instead as a transit corridor on their way west.

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Police in Bulgaria found the bodies of 18 migrants inside an abandoned truck.

To prevent people from entering the country illegally, Bulgaria's government erected a barbed-wire fence along its 259-kilometer border with Turkey. But foreigners fleeing poverty or conflict in their home countries manage to enter with the help of local people smugglers.

While the deaths of Europe-bound refugees and asylum-seekers at sea are more common, the grim discovery in Bulgaria is not the first time groups of migrants have been found dead in abandoned vehicles.

In October 2019, British police found the bodies of 39 people inside a refrigerated container that had been hauled to England. Police said all the victims, who ranged in age from 15 to 44, came from impoverished villages in Vietnam and were believed to have paid smugglers to take them on a risky journey to better lives abroad.

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Police said they died of a combination of a lack of oxygen and overheating in an enclosed space. The truck discovered in the town of Grays, east of London, had arrived in England on a ferry from Zeebrugge in Belgium.

Another similar tragedy took place in August 2015, when 71 migrants suffocated to death in the back of a refrigerated truck found on a highway in Austria.

A court in Hungary convicted an Afghan man and three Bulgarian accomplices in 2018 of being part of a criminal organization and committing multiple crimes, including human smuggling and murder, in connection with the deaths.

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Ten other defendants, mostly Bulgarians, were given prison terms ranging between three and 12 years.