BRUSSELS (AP) — A gunman fatally shot two Swedes in Brussels late Monday, prompting authorities to halt a Sweden-Belgium soccer match and leaving over 35,000 soccer fans holed up in the nearby national stadium as the capital went on its highest terror alert level with the assailant at large.

The killings happened some 3 miles (5 kilometers) from the stadium where over 35,000 fans were watching the Belgium-Sweden soccer, Belgium's anti-terror center said. The match was suspended half way through.

“The population needs to be actively vigilant and avoid any unnecessary travel,” anti-terror center spokeswoman Laura Demullier said, adding that the top priority for authorities was to get the thousands of fans safely out of the King Baudouin Stadium.

The center said the terror alert for the rest of the country was raised to its second-highest level. Raising the terror level in the capital to the top 4 rating means that a “threat is extremely serious.” It previously stood at 2, which means the threat was average.

“I have just offered my sincere condolences to @SwedishPM following tonight’s harrowing attack on Swedish citizens in Brussels," Prime Minister Alexander De Croo De Croo said. He added on X, formerly known as Twitter, “As close partners the fight against terrorism is a joint one.”

Eric Van Duyse, spokesman for the federal prosecutor’s office, told reporters the investigation was centering on “a possible terrorist motivation for the shooting.”

“During the evening, a claim of responsibility was posted on social media, having been recorded by a person claiming to be the assailant. This person claims to be inspired by Islamic State,” Van Duyse said. “The Swedish nationality of the victims was put forward as the probable motive for the act. At this time, no element indicates a possible link with the Israeli-Palestinian situation.”

Van Duyse would not say where the suspect might be or whether more than one person might have been involved. He said the suspected attacker was still at large.

As for the soccer match, he said, “security measures were urgently taken to protect the Swedish supporters.”

“A horrible shooting in Brussels, and the perpetrator is actively being tracked down,” said Interior Minister Annelies Verlinden, adding that she was joining government talks at the National Crisis Center.

Media reports aired amateur videos showing a man arriving on a scooter in an orange fluorescent vast, dropping the vehicle and immediately taking out a large weapon and opening fire on passersby. Apart from the two Swedes who were killed, a local taxi driver was hurt but his life was not in danger.

The shooting came at a time of increased vigilance linked to the ongoing Israel-Hamas war that has heightened tension in several European nations. At the same time, the Belgian capital has been the scene of increased violence linked to increasing international drug trafficking.

Sweden raised its terror alert to the second-highest level in August after a series of public Quran-burnings by an Iraqi refugee living in Sweden resulted in threats from Islamic militant groups.

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Associated Press writer Sam Petrequin contributed to this report.