Two Swedish nationals were shot to death and a third person was wounded in central Brussels, and a man who identified himself as a member of the Islamic State claimed responsibility in a video posted online.

The suspected assailant fled the scene after the shooting as a football match between Belgium and Sweden was about to start, triggering a massive manhunt and prompting Belgium to raise its terror alert to the highest level.

A Belgian federal prosecutor said there was no evidence that the attacker, who was still on the loose, had any link to the recent renewed conflict between Israel and Palestinian militants.

The likely motive for the attack was the Swedish nationality of the victims, the prosecutor said.

Sweden in August raised its terror alert to the second-highest level, warning of an increase in threats against Swedish interests abroad, after Koran burnings and other acts in Sweden against Islam's holiest text outraged Muslims and triggered threats from jihadists.

The suspected assailant, calling himself Abdesalem Al Guilani, claimed in a video on social media that he was a fighter for Allah. The federal prosecutor said the third victim, who was wounded but whose condition was not in life-threatening, was a taxi driver. The prosecutor called on Brussels' residents to stay indoors until the threat was over. European Commission staff were also advised to stay indoors.

Belgian Prime Minister Alexander de Croo confirmed on social media platform X, formerly known as Twitter, the victims were Swedish.

"I have just offered my sincere condolences to the Swedish PM following tonight’s harrowing attack on Swedish citizens in Brussels," de Croo said on X.

"Our thoughts are with the families and friends who lost their loved ones. As close partners, the fight against terrorism is a joint one," he said.

Sweden's Justice minister, Gunnar Strommer, told Reuters the government was working intensively with Belgian authorities to get more information about what happened.

All Swedes in Belgium will receive a text message sent to their phones urging them to be vigilant and to follow instructions from Belgian authorities, Swedish Prime Minister Ulf Kristersson said.

Belgium's interior minister said the investigation was in the hands of a federal prosecutor because of "a possible terrorist motive."

One Belgian newspaper said it was likely that the victims were two soccer supporters. Belgium were hosting Sweden in a Euro 2024 qualifying match on Monday evening. The match was suspended at halftime because of security reasons.

The shooting comes at a time of heightened security concerns in some European countries linked to the Israel-Hamas conflict. France is deploying 7,000 extra troops onto its streets after a teacher was fatally stabbed on Friday in an attack President Emmanuel Macron condemned as "barbaric Islamic terrorism."

Video footage of the Brussels attack posted on the Het Laatste Nieuws newspaper website showed a man in an orange jacket on a scooter at a street intersection with a rifle first firing two shots, then three more, then running into a building, firing two more shots, leaving, taking a few steps back again and shooting one more time.

One Belgium newspaper said a witness said the shooter shouted "Allahu Akbar" before the shots were fired.

According to a media transcript of the video message recorded by the self-declared perpetrator, he said:

"Islamic greeting Allahu Akbar. My name is Abdesalem Al Guilani and I am a fighter for Allah. I am from the Islamic State. We love who loves us and we hate who hates us. We live for our religion and we die for our religion. Alhamdulah. Your brother took revenge in the name of Muslims. I have killed 3 Swedes so far Al hamdoulelah. 3 Swedish, yes. Those to whom I have done something wrong, may they forgive me. And I forgive everyone. Salam Aleykoum."

France is tightening controls at the border with Belgium after the deadly attack in Brussels, Belgian media said.

Belgium's crisis centre warned the public not to make any unnecessary trips in the capital.