AFP — One person was killed and two police officers were seriously injured Saturday in a knife attack in eastern France that President Emmanuel Macron said was an “Islamist terror act.”

Prosecutors said three more officers were lightly wounded in the attack in the city of Mulhouse, carried out by a 37-year-old suspect who is on a terror prevention watchlist, prosecutor Nicolas Heitz told AFP.

The suspect was in custody.

France’s national anti-terror prosecutors unit (PNAT), which has taken charge of the investigation, said the suspect first attacked the municipal police officers, shouting “Allahu Akbar” (God is greatest).

Witnesses confirmed to AFP that the suspect had several times shouted the words in Arabic that are used by Muslims as an exclamation of their faith.

A civilian passer-by who intervened was fatally injured, the PNAT said in a statement. According to Mulhouse prosecutors, he was a 69-year-old Portuguese national.

Macron said there was “no doubt” that the incident was “a terrorist act,” specifically “an Islamist terrorist act.”

The government was determined to continue doing “everything to eradicate terrorism on our soil,” Macron added.

The terror watchlist, called FSPRT, compiles data from various authorities on individuals with the aim of preventing “terrorist” radicalization. It was launched in 2015 following deadly attacks on satirical magazine Charlie Hebdo’s offices and a Jewish supermarket.

One of the seriously wounded police officers sustained an injury to the carotid artery, and the other to the thorax, Heitz said.

French Interior Minister Bruno Retailleau was expected to travel to the scene of the attack later Saturday.

Police established a security parameter after the attack that happened shortly before 4:00 pm (1500 GMT) during a demonstration in support of the Democratic Republic of Congo in a busy part of Mulhouse, a city of around 110,000 inhabitants.

Military units were sent to the scene as backup and forensic scientists searched for evidence, working hurriedly to examine blood stains before rain could wash them away.

The suspect was born in Algeria and has been under judicial supervision and house arrest, with an expulsion order from France.

Retailleau told French broadcaster TF1 that France had tried to expel him 10 times, with the Algerians refusing each time to accept him.

“Horror has seized our city,” Mulhouse mayor Michele Lutz said on Facebook. The incident was being investigated as a terror attack, she said, but “this must obviously still be confirmed by the judiciary.”

The PNAT said it is investigating the attack for murder, and attempted murder “in connection with a terrorist enterprise.”

Macron, who spoke during a visit to France’s agriculture fair, said the “solidarity of the nation” was with the attack victim and his family.

French Prime Minister Francois Bayrou said that “fanaticism has struck again, and we are in mourning.”