A person known to the French authorities as a radical Islamist with mental health troubles stabbed a German tourist to death and wounded two people in central Paris on Saturday before being arrested, officials said.

The attack took place close to the Eiffel Tower during a busy late weekend night and came with the country on its highest alert for attacks as tensions rise against the background of the war between Israel and Hamas.

"We will not give in to terrorism," Prime Minister Elisabeth Borne wrote on X, formerly Twitter, after the attack.

French anti-terror prosecutors said that they would now take on the investigation.

The attacker was known to authorities as a radical Islamist and was being treated for mental illness, a police source told AFP.

- 'Violently threatened them' -

The Paris prosecutor's office said the attacker is French, born in 1997, and has been arrested in an investigation into murder and attempted murder.

Interior Minister Gerald Darmanin who visited the the scene by the River Seine's Bir Hakeim bridge said the man had already been sentenced in 2016 to "four years in prison" for planning another attack which he failed to carry out.

"A man attacked a couple who were foreign tourists. A German tourist who was born in the Philippines died from the stabbing," he said.

A taxi driver who witnessed the scene intervened, Darmanin said. The attacker then crossed the Seine attacking others and injuring one with a hammer, while police chased in pursuit.

Police used a taser to neutralise the man who was then arrested.

"He had threatened them very violently... he will now have to answer for his actions before justice," Darmanin said.

The suspect told police he could not stand Muslims being killed in "Afghanistan and Palestine", according to the minister.

- Tensions rising -

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

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

The country has suffered several attacks by Islamist 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 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 Islamist from Russia's Caucasus region.