Belgium raised its terror alert to the highest number after two Swedish nationals were killed in a shooting in central Brussels late Monday.
"Threat level 4 for the Brussels-Capital Region," the Belgian Crisis Centre wrote.
The victims are two Swedes, according to Prime Minister Alexander De Croo. The perpetrator is still being sought, Belgian Interior Minister Annelies Verlinden wrote on X. De Croo called on Brussels residents "to be vigilant."
The Euro 2024 qualifying match between Sweden and Belgium was abandoned after the first half with the score at 1-1.
The federal prosecutor's office has taken over the case "because of the possible terrorist motive of the shooting," the crisis center said.
"During the evening, the incident was claimed on social media. The message was recorded by a person identifying himself as the attacker. He claims to be inspired by Daesh terrorists.
"During the same message, the Swedish nationality of the victims was cited as a possible motive for the act," the center wrote.
It added that there was no indication of a link to the ongoing conflict in Gaza.
An armed man dismounted from a scooter in the north of the city and fired shots in the street, the Belga news agency reported.
When several people fled into a building entrance, he allegedly chased them and shot at them, the report said.
The police did not initially confirm this information.
De Croo said he had expressed his sincere condolences to the Swedish prime minister: "As close partners, the fight against terrorism is a common fight."
The Swedish national football team was playing a European Championship qualifier against Belgium on Monday evening in Brussels.
The match was later abandoned as a result of the shootings, the two national football associations wrote on the social media platform X, formerly Twitter.
Spectators in the stadium were asked to stay in their seats. "The Belgian police would like Swedish fans to stay in the arena for security reasons," the Belgian association wrote.
"Our thoughts are with all the relatives of those affected in Brussels," wrote the Swedish Football Association.
After 45 minutes, the match at the King Baudouin Stadium had been tied 1-1 after goals by Viktor Gyökeres in the 15th minute for Sweden and Romelu Lukaku in the 31st for the hosts.
News of the deaths of the two Swedes spread at half-time. According to the Swedish TV channel SVT, the players of Sweden's national team then decided not to continue the match. The Belgian national team players agreed with the move.
It was initially unclear whether and when the match would be continued. Belgium, as the leader of Group F, had already qualified for next year's European Championship in Germany, as had second-placed Austria. Sweden can no longer reach the first two places and thus cannot qualify directly.
About 20 minutes after the match should have started for the second half, the stadium loudspeakers announced that the match had been abandoned.
According to SVT, the team and supporters had to stay in the stadium for safety reasons because the alleged perpetrator had not yet been caught. "Stay calm and look out for each other," wrote the Swedish Football Association.
Belgian EU Council President Charles Michel wrote on X: "The heart of Europe is struck by violence. My condolences go to the families of the victims of the deadly attack in the center of Brussels."
Verlinden, De Croo and Justice Minister Vincent Van Quickenborne went to the National Crisis Centre in the evening to monitor the situation more closely.