Austrian police say the number of migrants found dead in a truck abandoned on a highway was 71, including 4 children, and 8 women.
Police also said on August 28 that three people had been arrested in Hungary in connection with the case.
Police found the refrigeration truck parked on the main highway connecting Vienna and Budapest on August 27.
German Chancellor Angela Merkel said the discovery had shaken European leaders discussing the migrant crisis at a Balkans summit in Vienna.
EU foreign policy chief Federica Mogherini said she hoped the tragedy would push member states to "take decisions and responsibility."
Serbian Foreign Minister Ivica Dacic put the onus on EU countries to find a better way to handle the influx of refugees.
Hundreds of thousands, many fleeing war in countries such as Syria and Libya, have made it into the European Union.
Germany alone expects 800,000 asylum-seekers this year, while Hungary is building a barbed wire fence along its border with Serbia aimed at keeping migrants out.
Meanwhile, the UN refugee agency UNHCR says the number of refugees and migrants crossing the Mediterranean to reach Europe has already passed 300,000 this year.
The UNHCR said that's up from 219,000 in the whole of 2014.
More than 2,500 people have died making the crossing this year, not including about 200 who are feared to have drowned off Libya in the last 24 hours.
That compares with 3,500 who died or went missing in the Mediterranean in 2014.
The Red Crescent said on August 28 that Libya has recovered 82 bodies washed ashore after a boat packed with migrants sank near the western town of Zuwara.