The missing Iraqi migrants were most likely picked up in Eisenhüttenstadt and driven away by relatives already living in Germany, said Frank Nürnberger, head of the town's reception facility, speaking with Rundfunk Berlin-Brandenburg.

While it remains unclear when exactly the refugees left the facility, unconfirmed reports stated that a number of people got into cars with license plates registered in Bielefeld.

Read more: German police find 51 migrants in Turkish truck

Two of the migrants found in the back of the truck reportedly stayed at the facility.

On Saturday, German police found 51 migrants, including 17 children, crammed inside the back of a Turkish truck on the border with Poland. Officers described the "harrowing image" from inside the truck, where all the travelers were thirsty and hungry, with some showing signs of dehydration. They were all taken to the Eisenhüttenstadt facility, while the truck's driver, a 46-year-old Turkish citizen, was detained.

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Investigators said they believe Saturday's discovery was part of a large smuggling ring operating along the German-Polish border region and that they were probing potential links to other smuggling incidents.

Just days earlier, police took 40 Iraqi refugees into custody after they had unlawfully entered Germany across the Polish border.

Despite tougher border controls along the so-called Balkan route, many migrants are still attempting to enter and seek asylum in Germany and other west European countries.

Smugglers based in the Balkans or Turkey often charge thousands of euros for the trip, forcing people to travel in overcrowded and often unreliable vehicles.

Read more: Combating human traffickers - facts and questions

According to the federal police, this year alone some 2,600 migrants have been smuggled across Germany's border with the Czech Republic, and a further 1,400 over the border with Poland. Despite the high numbers, authorities maintain there has not been a rise in the number of migrants being smuggled into Germany since Chancellor Angela Merkel's decision to effectively tolerate the arrival of hundreds of thousands of refugees in 2015. However, there has not been news of a reduction in the smuggling numbers, either.

Saturday's discovery was reminiscent of a disturbing incident in Austria during the height of the migrant crisis two years ago, when authorities uncovered the dead bodies of 71 migrants inside an abandoned freezer truck. The refugees are believed to have suffocated as they were being smuggled into Western Europe.