A man suspected of stabbing a German tourist to death near the Eiffel Tower was to appear before a French judge on Wednesday with a view to being charged with carrying out a terror attack, a source close to the case said.
The deadly assault late on Saturday came with France at its highest alert level against the background of the war between Israel and Palestinian militant group Hamas.
It followed a series of recent isolated attacks in the country.
The incident has increased security concerns in the run-up to the Paris Olympic Games that begin in July.
The case is being handled by French anti-terrorist prosecutors who have opened an investigation into a "terrorist" plot.
Armand Rajabpour-Miyandoab, a French national born in 1997 to Iranian parents, is a known Islamist radical who has sworn allegiance to the Islamic State group and was under psychological surveillance for mental health issues.
He was arrested over the killing of a 23-year-old man, identified as a German-Filipino citizen, with two blows from a hammer and four from a knife, as well as wounding two others.
Rajabpour-Miyandoab will in the afternoon appear before the investigating magistrate who is then expected to formally charge him ahead of trial, the source said.
He told investigators he acted "in reaction to the persecution of Muslims around the world", a source close to the investigation said, describing him as "very cold" during questioning.
He said he picked the Eiffel Tower as "he could not bear it being lit up in the colours of the Israeli flag", the source said.
French authorities had displayed solidarity with Israel after the October 7 attacks by Hamas that killed 1,200 people, mostly civilians, according to Israeli authorities, and saw some 240 hostages taken.
An Israeli bombardment has since killed more than 16,000 people in Gaza, most of them women and children, the Hamas-run government there says.
Rajabpour-Miyandoab, whose family is not religious, converted to Islam at 18 and began consuming huge amounts of IS propaganda, according to prosecutors.
A woman known to the authorities who Rajabpour-Miyandoab is said to have met the night before the attack was also detained for questioning but released without charge at this point, the source close to the investigation said.
A source close to the case said that the 27-year-old woman belonged to the "jihadist sphere" and had recently received a marriage proposal from the suspect.
He had previously been sentenced to five years in prison in 2016 for planning an attack, before he was released in 2020.
France's Interior Minister Gerald Darmanin said on Monday that there had been a "psychiatric failure" in his case, as "doctors said on several occasions that he was doing better".
He said regional authorities did not have the power to issue an administrative order for such an individual to undergo psychiatric treatment, and "this has to change".
Rajabpour-Miyandoab's mother had reported concerns about him as recently as October, but there was insufficient proof at the time to take legal action.
An account Rajabpour-Miyandoab opened on X, formerly Twitter, in October showed "many posts about Hamas, Gaza or Palestine more generally", according to France's top anti-terror prosecutor Jean-Francois Ricard.
On it he posted a video in Arabic, presenting himself as an IS fighter based in Afghanistan.
Rajabpour-Miyandoab had been radicalised through contacts on the Internet and had been in touch with perpetrators of similar past attacks, Darmanin said.
These contacts included a radicalised Islamist from Russia's northern Caucasus region who would later kill teacher Samuel Paty, beheaded outside his school near Paris in 2020.
