PARIS: French prosecutors have opened an investigation into a "terrorist plot" after a man known to the authorities as a radical with mental health troubles stabbed a tourist to death and wounded two other people in central Paris at the weekend before being arrested.

The attack around 9:00 pm (2000 GMT) Saturday near the Eiffel Tower came as France is at its highest alert level against the background of the war between Israel and Hamas.

Terrorism prosecutors told AFP on Sunday they were investigating the knife and hammer attacker, identified as Armand Rajabpour-Miyandoab, a French national born in 1997 to Iranian parents.

One dead, two injured after man attacks tourists near Paris' Eiffel Tower

Arrested at the scene, he is suspected of murder and attempted murder "in connection with a terrorist plot".

A 23-year-old man, identified by a judicial source as a German-Filipino citizen, died in the attack, though a taxi driver intervened to keep the attacker away from his wife.

Patrick Pelloux, an emergency doctor on duty at the time of the attack, said the couple were both nurses, adding that the woman was severely shocked but unhurt.

A 66-year-old British citizen and a 60-year-old French national were wounded in the attack.

Health Minister Aurelien Rousseau told broadcaster France 3 that the wounded victims suffered only "superficial (physical) traumas, but of course psychological traumas that will be enormous".

Prosecutors announced a press conference for 7:30 pm on Sunday to give updates on the investigation.

Three people "close to" Rajabpour-Miyandoab were being held in custody on Sunday afternoon, prosecutors said.

Meanwhile government leaders including Prime Minister Elisabeth Borne and Interior Minister Gerald Darmanin were to hold a security meeting.

"We will not give in to terrorism," Borne wrote on X, formerly Twitter, while President Emmanuel Macron offered his condolences to the family of the man killed.

Rajabpour-Miyandoab, known to authorities for extremism, shouted "Allahu Akbar" -- Arabic for "God is greatest" -- as he struck on Saturday, Darmanin said at the scene by Bir Hakeim bridge over the River Seine.

The suspect, who lived with his parents in the Essonne region south of Paris, told police he could not stand Muslims being killed in "Afghanistan and Palestine" and accused France of being "an accomplice to what Israel is doing" in the Gaza Strip, Darmanin added.

German Chancellor Olaf Scholz wrote on X that he was "devastated" by the attack, saying that "our thoughts are with the wounded, their families and friends".

His Interior Minister Nancy Faeser had earlier warned that "the war in Gaza after Hamas' terrorist act (of October 7) has worsened the threat," saying that "the threat of terrorism is acute and serious".

Police and security sources confirmed the attacker had claimed responsibility in a social media video as he struck, speaking about "current events, the government (and) the murder of innocent Muslims".

Investigators would scrutinise his medical history, a security source told AFP, saying the attacker was "very unstable and easily influenced".

Rajabpour-Miyandoab was "being monitored in a way that did not mean he was being hospitalised, he was supposed to follow a course of treatment" for his mental health issues, said Rousseau, the health minister.

"As often in these cases, there's a mixture of an ideology, an easily influenced person and, unfortunately, psychiatry," he added.

Darmanin said the man had previously been sentenced in 2016 to four years in prison for planning another attack in the Paris business district of La Defense, which he failed to carry out.

Joseph S., a 37-year-old supermarket manager who asked not to give his last name, witnessed the attack as he sat in a bar.

He heard screams and people shouting "help, help" as they ran. A man wielding a hammer attacked a man who had fallen down, and within five to 10 minutes the police arrived, he told AFP.

The country has suffered several attacks by extremists, including the November 2015 suicide and gun attacks in Paris claimed by the Islamic State group in which 130 people were killed.

There had been a relative lull in recent years, even as officials have warned that the threat remains.

But tensions have risen in France, home to large Jewish and Muslim populations, following Hamas's attack on Israel on October 7 and Israel's subsequent bombardment of the Gaza Strip.

Security in Paris is also under particular scrutiny as it gears up to host the 2024 Summer Olympic Games.

In October, teacher Dominique Bernard was killed in the northern French town of Arras by a young radicalised from Russia's Caucasus region.