Turkish police rescued 57 Pakistani migrants who had been chained up in an Istanbul basement by human traffickers trying to extort money, local media reported on Tuesday.

The traffickers told the migrants that they would take them to Europe for $10,000, with the money to be paid after they arrived, according to Hurriyet daily.

Some of those found on Monday had been tortured, the newspaper added.

Police also detained three traffickers of Pakistani origin on suspicion of misleading the migrants during the raid on the European side of the city.

The migrants had reportedly hoped to reach Europe via Greece or Italy, giving a code to the traffickers to access the money upon reaching Europe, Hurriyet said.

However, the human trafficking gang mainly made up of Pakistanis demanded the $10,000 upfront and told the migrants chained in Istanbul to call their families to tell them they had reached Europe already and to transfer the money, the daily said.

The incident comes days after bullet-riddles bodies of 20 people attempting to illegally cross into Iran on their way to Europe via Turkey were found near Balochistan's Turbat area in two separate incidents.

The Balochistan Liberation Front (BLF) had claimed responsibility for the deaths and an alleged BLF commander suspected of involvement in one of the incidents was later killed during an intelligence-based operation by Frontier Corps (FC). Human traffickers were also arrested in separate operations in Punjab.

Hundreds of thousands of migrants including Syrians, Iraqis, Pakistanis and Afghans have entered Europe in recent years.

At the height of the refugee crisis in 2015, over a million migrants arrived in Europe by sea, though the numbers have declined since a 2016 deal between Turkey and the European Union.