Migrants attend a candlelight ceremony at a railway station in memory of 71 refugees who died in a truck found in Austria, in Budapest, Hungary, Aug.  28, 2015.
Migrants attend a candlelight ceremony at a railway station in memory of 71 refugees who died in a truck found in Austria, in Budapest, Hungary, Aug. 28, 2015.

Austrian and Hungarian law-enforcement officials say several people have been arrested in connection with the discovery of 71 bodies of migrants found in a truck trailer on an Austrian highway near the border with Hungary.

Austrian officials said three people were arrested — two Bulgarians and a third person with Hungarian identity papers.  Later Friday, their Hungarian counterparts said four people were in custody — three Bulgarian citizens and an Afghan national. There were was no immediate explanation for the discrepancy.

Austrian police also say their initial estimate of the number of dead was too low.  On Thursday they announced 20 to 50 victims had been found; on Friday the number was raised to 71. The victims — 59 men, eight women, and four children — are believed to have suffocated in the refrigerated truck.

Investigators stand near a truck that stands on
Investigators stand near a truck that stands on the shoulder of the highway A4 near Parndorf south of Vienna, Austria, Thursday, Aug 27, 2015.

The chief of police of Austria's Burgenland province, where the bodies were found, said a Syrian travel document was found among the bodies, suggesting that at least some of the victims were fleeing the civil war in Syria.

Vienna meeting

Thursday's discovery of the bodies came as western Balkan leaders met in Vienna to discuss ways to stem Europe's worst migration crisis since World War II. German Chancellor Angela Merkel was among leaders attending the summit.

Merkel called the discovery a warning to Europe to come to grips with the migrant crisis, which this year has reached an intensity not seen since World War II.

U.N. chief Ban Ki-moon says he is "horrified and heartbroken".

Many of the victims were Syrians, including children, looking to escape war, terrorism, and hopelessness for a better life in Europe.

"The Syrian war has just been manifested on a roadside in the heart of Europe,"  Ban said Friday.

Serbia and Macedonia have become major transit countries for tens of thousands of migrants trying to reach European Union countries.

Last week, Macedonia, which currently is dealing with 3,000 migrants arriving every day from EU member Greece, declared a state of emergency.

EU members Greece and Italy, and non-EU Balkan countries such as Macedonia and Serbia, are dealing with much of the initial refugee burden through sea and land routes. But many of the migrants are destined for Western European countries, among them Germany and Austria.

Austrian plan

Austrian Foreign Minister Sebastian Kurz suggested a five-point plan Thursday that foresees establishing safe havens in the region where those seeking asylum in the EU could be processed and — if they qualify — be given safe passage to Europe.

Kurz spoke on the sidelines of the conference that is primarily focused on ways of getting a grip on the migrant influx that threatens to overwhelm some countries while leaving others relatively unaffected.

Beyond safe havens, to be protected by troops acting under a U.N. mandate, the Austrian plan to be submitted to EU decision makers foresees increased controls on Europe's outer borders and coordinated action against human smuggling.

The U.N. refugee agency is calling on all governments to respond compassionately to the human tide of people who have been displaced from their homelands and are now seeking safety.

The UNHCR say more than 300,000 refugees and migrants have made the perilous journey across the Mediterranean this year, trying to reach Europe.  This is a huge increase over the 219,000 who made the crossing during the whole of 2014.

Meanwhile, some 2,500 refugees and migrants have died or gone missing.