Two Swedish nationals were shot dead on Monday evening in central Brussels by a single armed man, in what Prime Minister Alexander de Croo of Belgium said was an act of terrorism.

The suspect in the killing was fatally shot by police on Tuesday morning after an overnight search, the office of Belgium’s public prosecutor said.

The suspect, a man whose name was not released, died in a hospital, the prosecutor’s office said. A weapon was found at the scene after the man was shot, according to the interior minister.

Belgium’s justice minister, Vincent Van Quickenborne, said on Tuesday that the suspect, a Tunisian man who was living in the country illegally, had been known to authorities for possible radicalization and criminal activity since 2016, but the authorities had not acted on mounting intelligence that he posed a threat.

“I have just offered my sincere condolences to @swedishpm following tonight’s harrowing attack on Swedish citizens in Brussels,” de Croo said on X, formerly known as Twitter, referring to the Swedish Prime Minister. “Our thoughts are with the families and friends who lost their loved ones. As close partners, the fight against terrorism is a joint one.”

The victims were wearing Sweden soccer shirts, local media reported, and may have been preparing to attend a match between Sweden and Belgium at a major stadium in northern Brussels.

An unverified video of the attack circulating on social media showed a man in a white helmet and a high-visibility orange jacket pursuing and shooting at his victims who ran into a building, and then shooting them again at closer range, execution style.

Another unverified video circulating on social media, shot in selfie mode, showed a man speaking in Arabic and describing himself as an adherent to the Islamic State group.

“So there has been a claim via social media where someone says he is the perpetrator, that he has sympathies for IS, and what is also important, he mentions the Swedish nationality of those victims,” Eric Van Der Sypt, a spokesperson for the federal prosecutor’s office, told the Belgian broadcaster VTM. “For now, at the current stage of the investigation, there would be no relationship to the conflict in Gaza,” he added.

Van Der Sypt, in comments to the Belga news agency, said that a third man, a taxi driver, had been injured in the attack but was being treated in a hospital and out of danger.

The threat level in Brussels was raised to level four, the highest, in the region, and France was tightening controls at its border with Belgium, France’s interior minister, Gérald Darmanin, said.