The bodies of between 20 and 50 migrants were found in a truck in Austria on Thursday, highlighting the dark side of Europe's migrant crisis as regional leaders struggle to stem the massive flow of people desperately trying to reach the EU.
The gruesome discovery on a motorway near the Slovakia and Hungary borders was thought to be the worst tragedy on land in Europe's worst migrant crisis since 1945.
Police said the vehicle -- which had the markings of a Slovakian poultry company and bore Hungarian number plates -- contained between 20 and 50 bodies.
It was not yet clear how they had died.
"Today is a dark day... This tragedy affects us all deeply," Interior Minister Johanna Mikl-Leitner said at a press conference.
She said Austria would tighten border controls and intensify police checks on international trains, and called on the other 27 EU member states to show "zero tolerance" for people smugglers.
The deaths came a day after at least 55 migrants were found dead in stricken boats in the Mediterranean, adding to a toll of more than 2,300 people who have drowned while attempting to reach Europe by sea.
German Chancellor Angela Merkel and Balkan leaders, meeting in Vienna to discuss how to tackle the escalating crisis, reacted with shock to the Austrian tragedy.
"We were all shaken by the horrible news that up to 50 people lost their lives because they were in a situation where people-smugglers did not care about their lives," Merkel said.
"This is a warning to us to tackle this migrants issue quickly and in a European spirit, which means in a spirit of solidarity, and to find solutions."
- Western Balkans route -
European leaders have come under fire for failing to tackle the arrival of several hundred thousand migrants this year, many fleeing hotspots such as Syria, Iraq and Afghanistan.
The western Balkans has become a major route for migrants and refugees trying to cross over into EU member state Hungary. Most then try to make it to wealthier European countries like Germany and Sweden.
Speaking at the Vienna meeting, Serbia's Foreign Minister Ivica Dacic said outside money provided so far was insufficient to handle the large numbers.
"This is a problem of the European Union and we (the transit countries) are expected to come up with an action plan," Dacic said.
"I think the European Union has to come up with a plan first," he said. "I have to be very direct here. Please understand, we are bearing the brunt of the problem."
This was echoed by his counterpart from Macedonia, which last week declared a state of emergency and shut its border with Greece for three days after being unable to cope.
"Unless we have a European answer to this issue, none of us should be under any illusion that this will be solved," Nikola Poposki said.
Reiterating his call for a reform of the Dublin Accords "to distribute refugees fairly within the EU", Germany's Foreign Minister Frank Steinmeier said Berlin would contribute one million euros to help the Balkans cope with the migrants, as well as food and other supplies.
But he also called on governments there "to help manage the expectations of your citizens and provide them with a realistic picture of their virtually non-existent chances of being granted asylum in Germany."
Almost 40 percent of asylum-seekers in Germany are from the western Balkan countries, Steinmeier said.
- Hungary barrier -
The daily number of people crossing into Hungary hit a record 3,000, including nearly 700 children, latest police figures showed.
Lawmakers are set to debate next week whether to deploy troops to stem the influx, after violence erupted briefly at a refugee processing centre near the Hungarian border town of Rozke.
Alarmed by the growing humanitarian disaster, UN chief Ban Ki-moon has urged countries "in Europe and elsewhere to prove their compassion and do much more to bring an end to the crisis".
UN refugee chief Antonio Guterres and French Interior Minister Bernard Cazeneuve called for the urgent creation of more so-called "hotspots" -- processing centres to sort refugees fleeing war from economic migrants who are simply in search of a better life.
Hamstrung by a lack of a coherent European response, governments have at times taken contradictory approaches to the problem.
While Hungary's right-wing government is building a 175-kilometre (110-mile) razor-wire barrier to keep migrants out, a Czech minister has called for the passport-free Schengen zone to be closed with the help of NATO troops.
Meanwhile Germany, which is preparing to receive a record 800,000 asylum-seekers this year, has eased the application procedure for Syrians fleeing the brutal civil war.
But Berlin's largesse has not been welcomed by everyone at home, particularly in the east where a spate of attacks has targeted refugee centres.
On a visit to a migrant shelter in the eastern town of Heidenau, Merkel was greeted by about 200 protesters, some booing and shouting "traitor, traitor" and "we are the mob".
However, she vowed: "There will be no tolerance of those who question the dignity of other people."