Five-year-old twin girls and a 6-year-old boy, all from Syria, were in life-threatening condition and taken immediately to the hospital in Braunau, Mr. Furtner said. Their conditions have since improved, he said.

The driver, a 29-year-old Romanian, has been arrested, Mr. Furtner said.

The grisly discovery of bodies near Vienna has drawn international attention to the trafficking business behind the migration of tens of thousands of people fleeing war and despair in the Middle East, Africa and Asia.

On Saturday, three Bulgarians and one Afghan who are suspects in that fatal smuggling case appeared in court in Kecskemet, Hungary, and were ordered to remain in detention pending trial on charges of human trafficking involving torture and financial gain. Officials would not release their identities, and provided few details, but said the suspects had picked up the 71 migrants on the Serbian border.

Ferenc Bicskei, president of the Kecskemet regional court said in a news conference that the local courts had lately been seeing 25 to 30 human smuggling cases each month, and that in response sentences would be more severe.

During the past day, the Hungarian police said, they had detained 2,822 people who crossed the border illegally and started criminal proceedings against 13 smugglers who had tried to drive migrants, crammed in trucks, through the country.