Hungarian prosecutors yesterday moved to detain for one month three Bulgarians and one Afghani citizen suspected to have transported 71 refugees who were found dead in a truck by an Austrian motorway on Thursday.

The victims, 59 men, eight women and four children are thought to be mainly Syrians.

Police were alerted when a road worker saw liquid seeping from the vehicle and the badly decomposing bodies were found in its refrigerated compartment. Police suspect the vehicle found its way there as part of a Bulgarian-Hungarian human smuggling network.

The deaths caused an international outcry and highlighted the dangers facing hundreds of thousands of refugees who have chosen to flee violence and poverty in the Middle East and Africa and try to settle in the European Union. On the same day the lorry was found, it emerged that up to 300 refugees were feared dead after two boats sank off Libya.

Yesterday the suspects in the truck case, handcuffed and each carrying a bottle of water, were escorted by special police forces to the court house in the central Hungarian town of Kecskemet, where the truck began its final journey.

A prosecution spokesman told journalists the four faced human trafficking charges involving torture and targeting financial gain.

"The truck left from Kecskemet, picked up the refugees near the southern border (with Serbia), then ferried them through Hungary to Austria," said prosecution spokesman Gabor Schmidt.

The four face prison terms ranging from two to 16 years each.

The four suspects are not being charged with manslaughter in Hungary because they will face that charge in Austria, he said.

The four men arrived at the court house in four separate police vehicles. One older, heavy-set man in his late 40s and three younger men in their 20s or 30s emerged from the vehicles with a heavy police escort.

The court has convened to approve the detention for a one-month period, which can be prolonged indefinitely.

So far this month more than 40,000 asylum seekers, the majority of them Syrian, have arrived in Hungary from the Balkans.

Many fall prey to smugglers who wait near the refugee camps, offering to take them at a high price on to western Europe.

The gruesome lorry discovery and other tragedies prompted UN Secretary-General Ban Ki-moon to call on Friday for more concerted action to alleviate Europe's migrant crisis.

Ban called for a "collective political response" to avert "a crisis of solidarity".

He called on states involved to "expand safe and legal channels of migration".

"A large majority of people undertaking these arduous and dangerous journeys are refugees fleeing from places such as Syria, Iraq and Afghanistan," he said.

"The international community must also show greater determination in resolving conflicts and other problems that leave people little choice but to flee," he added.

The UN Secretary-General called on nations to observe international law on asylum requests, and not to "force people to return to places from which they have fled if there is a well-founded fear of persecution. This is not only a matter of international law; it is also our duty as human beings," Ban said.