At least 350 Pakistanis were on board a packed trawler that capsized off southern Greece on 14 June, Pakistan’s interior minister says.
Rana Sanaullah told parliament his estimate was based on families who had sought government help and had taken DNA tests.
Egyptians and Syrians were also among the hundreds of migrants feared dead.
The official death toll remains at 82, while 104 survived, including 12 Pakistanis.
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Giving his estimate, Mr Sanaullah said that for Pakistan “perhaps there has never been such a large toll in any incident before, even in terrorist incidents”.
The boat is thought to have set off from Egypt and picked up passengers in the Libyan city of Tobruk who paid thousands of dollars for the trip. The UN says between 400 and 750 people could have been crammed onto the vessel, which sank about 50 miles (80km) southwest of the coastal town of Pylos.
It is one of the worst migrant boat disasters in the Mediterranean in recent years, and questions remain about the Greek response after it became clear that the boat was in trouble.
Shipping data suggests the fishing vessel was not moving for at least seven hours before it capsized.
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On Thursday Pakistan’s Federal Investigation Agency (FIA) spoke of at least 209 Pakistani victims, based on DNA samples collected mainly from families in Punjab, and some from Pakistan-administered Kashmir.
More than 20 suspected human traffickers have been arrested in Pakistan since the disaster.
Greece has charged nine Egyptian men with human trafficking over the shipwreck. They have denied wrongdoing.