Austrian police have stepped up security in Vienna and other cities after receiving a warning of possible attacks during the holiday season.
A statement issued by Vienna police said:
In the lead-up to Christmas, a friendly intelligence service sent a warning to numerous European capitals saying potential bomb or gun attacks could take place in areas with large crowds between Christmas and New Year
The warning included "several names of potential attackers" but investigations have so far yielded no concrete results, the statement said.
Border controls have been tightened in Austria as authorities try to clamp down on human trafficking.
The interior ministry said tougher checks were being put in place at eastern borders after 71 migrants were found dead in the back of a lorry abandoned on an Austrian motorway.
Huge queues formed on a Hungarian motorway leading to Austria as the new checks were introduced.
Traffic was jammed for 12 miles on the country's M1, according to local media.
"We will do controls for an undetermined length of time at all important border crossings in the eastern region, looking at all vehicles that have possible hiding places for trafficked people," minister Johanna Mikl-Leitner told local radio.
A fifth suspect has arrested in connection with the discovery of the bodies of 71 migrants in back of a lorry found abandoned on an Austrian motorway.
The Bulgarian citizen is also under suspicion of human trafficking, Hungarian police said.
Meanwhile, postmortems have been carried out on 16 of the bodies and it is presumed they suffocated, Austrian police said.
"We are still awaiting the final report from the forensic team, but it looks like they have suffocated," said police spokesman Gerald Pangl.
Governments must do "much more" to solve the migrant crisis, the UN's Secretary-General has said.
Ban Ki-moon said he was "horrified and heartbroken" by the recent deaths, including the "grim" discovery of 71 bodies in a lorry found abandoned on an Austrian motorway.
He said: "I commend those leaders and communities who have stepped up to our shared responsibilities and obligations. But much more is required.
"I appeal to all governments involved to provide comprehensive responses, expand safe and legal channels of migration and act with humanity, compassion and in accordance with their international obligations.
"Let us do all we can to provide people in the most desperate circumstances with a measure of safety and a sense of hope."
Earlier, Hungarians held a vigil for the victims of the Austrian discovery outside Budapest's main train station, where thousands of migrants have been sheltering for weeks.
The CEO of the Refugee Council has said there "needs to be political will" to end the current forced migration crisis after the last two days saw an abandoned van in Austria discovered with 71 bodies inside and another migrant boat capsize off the coast of Libya .
Describing the events as "shocking" but "hardly surprising" Maurice Wren told ITV News it was the responsibility of EU leaders to create "safe and legal routes for people who are fleeing persecution and harm."
Here is a summary of what we know so far following the discovery of 71 bodies in the back of an abandoned lorry in Austria yesterday.Read the full story ›
A fourth suspect has been arrested in connection with a lorry that was found abandoned in Austria with 71 bodies inside.
Hungarian police confirmed that three Bulgarians and one Afghan citizen had been arrested.
The body of a "one to two-year-old girl" has been discovered in the back of an abandoned lorry in Austria.
Police confirmed the toddler was among 71 people, including four children, that had been found dead in the back of a lorry which authorities believe had been parked on the edge of an Austrian motorway for more than 24-hours before it was spotted.
Police chief Hans Peter Doskozil told a press conference today: "One of the children is a one to two-year-old girl and one child is an eight to nine-year-old boy."
The 71 people who were found dead in an abandoned lorry in Austria yesterday died of suffocation, according to the Austrian police chief heading up the investigation.
Police chief Hans Peter Doskozil also confirmed the passengers in the lorry were suspected migrants as a "Syrian travel document" was found in the vehicle.
Speaking at a press conference today Doskozil said authorities believed the lorry had been parked on the highway for at least 24 hours before it was discovered and a Bulgarian-Hungarian trafficking ring was thought to be behind the deaths.
The death toll following the discovery of an abandoned lorry full of bodies in Austria has risen to 71.
According to reports the victims, who police suspect had come from Syria, included a two-year-old girl.
During a press conference today an Austrian police chief confirmed the dead included:
- 59 men
- 8 women
- 4 children