Death was in the air Friday, its stench overpowering as workers on Austria's border with Hungary unloaded the bodies of some of the 71 migrants who perished trapped in a truck they hoped would take them to a better life.

Found Thursday on the main Austrian highway leading to Hungary, the truck containing the victims' corpses was towed to a cooled border warehouse before police and forensic experts began the gristly work of unloading the partially decomposed bodies before shipping them to a Vienna morgue for autopsies.

On Friday, workers continued the work, wearing gloves and respirators as they hefted plastic body bags into coffins neatly lined up on the warehouse ramp. One after another five trucks backed up to be loaded.

Moments after the last truck left in the direction of Vienna, about a dozen migrants scurried across a patch of the four-lane highway connecting Vienna to the Hungarian capital, Budapest.

They said they were Kurds from Syria and Iraq. Two were women carrying small babies. All seemed exhausted.

No, they said: they hadn't heard about the deaths.

As the trucks sped toward Vienna, police in Austria and Hungary worked to trace the perpetrators, announcing the arrests of several suspects.

Austrian police said three people had been arrested while their Hungarian counterparts said four were in detention. There was no immediate explanation for the discrepancy.

This year has seen tens of thousands of people risking everything to seek a better life or refuge in wealthy European countries. At least 2,500 have died, mostly at sea, where another tragedy was unfolding Friday as Libyan authorities counted bodies from two ships that capsized off the coast of that country. The U.N. refugee agency said 200 were missing and feared dead.

In Austria, officials said they are still investigating but believe the migrants suffocated. Investigators found a Syrian travel document, indicating that at least some of the dead were refugees fleeing violence in Syria.

The 71 included eight women and four children, the youngest a girl between 1 and 2 years old, the others boys aged 8 to 10. Authorities initially estimated the death toll at 20 to 50, but raised it after officials counted the bodies at the warehouse.

Migrants fearful of death at sea in overcrowded and flimsy boats have increasingly turned to using a land route to Europe through the Western Balkans. They start in Greece, which they can reach via a short boat trip from Turkey, then move on through Macedonia, Serbia and into Hungary, where thousands have been crossing the border every day, crawling over or under a razor-wire fence meant to keep them out.

Most go from there to other countries in the European Union, sometimes paying smugglers to drive them, but the discovery of the bodies in the truck showed there is no truly safe path.

Police in Hungary said that as of Tuesday, 776 suspected human smugglers had been detained this year, compared to 593 in all of 2014. In the southern part of the country, police said they had found 18 Syrians near an overturned van on the M5 highway between Szeged and Budapest early Friday. Ten were taken to the hospital for treatment while the driver, a Romanian, was treated for hand injuries and then taken into custody on suspicion of human smuggling.

Hungarian police also said that over the last several days, 21 suspected human traffickers — 16 Romanians, two Syrians, two Hungarians and a Russian citizen — had been arrested and 16 vehicles carrying around 100 migrants toward the West had been confiscated.

Volunteers, tending to hundreds of migrants a day in a transit zone set up at Budapest's Keleti train station, asked people to bring candles and flowers to a tribute to be held there Friday evening in memory of the 71 victims.

The truck with the 71 migrants inside was found parked in the safety lane of the highway from Budapest, Hungary, to Vienna on Thursday. It was not clear how long the bodies had been in it, but police believed they may already have been dead by the time the truck crossed the border into Austria overnight Wednesday. Autopsies were being conducted, said state prosecutor Johann Fuchs, with results expected in several days.

Fuchs said the perpetrators could be charged with human smuggling, danger to public safety leading to death, or murder.

Austrian police said that two of the three arrested are Bulgarian citizens, while the third has Hungarian identity papers. One is the truck owner, while two others were apparently taking turns driving, said Hans Peter Doskozil, chief of police in Burgenland province, where the truck was found. He said police believe that the suspects were part of a larger Bulgarian-Hungarian human smuggling ring.

In Budapest, Hungarian national police spokeswoman Viktoria Csiszer-Kovacs said four people — three Bulgarian citizens and one from Afghanistan — were in custody in connection with the deaths. She said the Afghan had a Hungarian identification document but was not a Hungarian citizen.

Csiszer-Kovacs said two Hungarian police detectives were working with authorities in Austria on the case.

The International Organization for Migration reports that in 2014, Austria received around 28,000 applications for asylum, a number already reached this year by the end of June. Projections for this year are for 80,000 asylum applications.

Interior Minister Johanna Mikl-Leitner said the tragedy "should serve as a wake-up call ... for joint European action" in dealing with the torrent of migrants flocking to Europe. Melissa Fleming, spokeswoman for the U.N. refugee agency in Geneva called the tragedy "absolutely shocking."

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Jahn reported from Vienna. Associated Press Writer Alison Mutler in Bucharest, Romania; Pablo Gorondi in Budapest, Hungary; and Jamey Keaten in Geneva contributed to this report