Austria’s top security official said that least one "Islamist terrorist" was suspected as having been involved in the shooting attack in Vienna late Monday.
The attack has killed at least four people and injured several others.
"We experienced an attack yesterday evening from at least one Islamist terrorist," Austrian Interior Minister Karl Nehammer told reporters at an early Tuesday morning news conference.
"Austria for more than 75 years has been a strong democracy, a mature democracy, a country whose identity is marked by values and basic rights, with freedom of expression, rule of law, but also tolerance in human coexistence. Yesterday's attack is an attack on just these values."
Nehammer said that initial investigations suggest the suspect was a sympathizer of the ISIS terrorist group. The suspected attacker was wearing an explosives belt that turned out to be fake during the attack, and was later shot to death by police, he said.
He did not elaborate further, citing the ongoing investigation. Authorities are still trying to determine whether further attackers may be on the run.
Police confirmed on Tuesday that three civilians were killed in the attacks—two men and one woman—with 15 others wounded, including a police officer. News agency APA later reported a fourth civilian had died.
The public has been urged by top officials to remain home on Tuesday. Vienna Mayor Michael Ludwig told broadcaster ORF that there will be a tougher police presence on Tuesday.
Gunmen attacked six locations in central Vienna on Monday evening shortly after 8 p.m. local time, starting outside the main synagogue in the city center. People were out in the city for the last night before a nationwide COVID-19 lockdown was expected to go into effect.
Authorities have called the incident a terrorist attack and said that people have uploaded around 20,000 videos of the Monday attack to police.
Witnesses described the men firing into crowds in bars with automatic rifles, Reuters reported.
Unverified footage on social media showed gunmen walking through the streets, apparently shooting at people at random, wounding several, reported The Associated Press. One video showed a man gunning down a person outside what appeared to be a bar on the street housing the synagogue, Reuters reported.
Police sealed off much of the historic center of Vienna overnight. Many people checked into bars and hotels, while public transport throughout the town was shut down.
"It is the hardest day for Austria in many years. We are dealing with a terror attack the severity of which, thank God, we have not experienced in Austria in many years," Nehammer told a news conference late Monday.
Austria's capital had so far been spared the kind of deadly terrorist attacks that have struck Paris, London, Berlin, and Brussels, among others, in recent years.
Rabbi Schlomo Hofmeister, who told London's LBC radio that he was living in the compound of the synagogue, said that while looking down from the windows he saw gunmen shooting at guests of various bars and pubs in the city.
"The gunmen were running around and shooting at least 100 rounds or even more in front of our building," he told the radio station.
“We are victims of a despicable terror attack in the federal capital that is still ongoing,” Austria's Chancellor Sebastian Kurz said hours after the attack.
“One of the perpetrators was neutralized, but several perpetrators appear to still be on the loose,” he said. “They seem to also, as far as we know, be very well equipped, with automatic weapons. So they were very well prepared."
Condolences have come in from around the world, with top officials from the European Union, France, Norway, Greece, and the United States expressing their shock at the attacks.
"These evil attacks against innocent people must stop. The U.S. stands with Austria, France, and all of Europe in the fight against terrorists, including radical Islamic terrorists."