PARIS/BRUSSELS (Reuters) - French police have arrested a man suspected of involvement in the shooting deaths last weekend of three people at Brussels' Jewish Museum, officials said on Sunday.
The 29-year-old was arrested in the southern French city of Marseille on Friday and had a Kalashnikov and another gun with him, a French police source said.
The man, named by the source as Mehdi Nemmouche, was from the northern French city of Roubaix.
French media reported that he was suspected of having stayed in Syria with jihadist groups in 2013.
An Israeli couple and a French woman were killed on May 24 when a man entered the Jewish Museum in busy central Brussels and opened fire with a Kalashnikov rifle. A Belgian man remains in critical condition in hospital.
French President Francois Hollande confirmed a suspect had been arrested and said France was determined to do all it could to stop radicalised youths from carrying out attacks.
"We will monitor those jihadists and make sure that when they come back from a fight that is not theirs, and that is definitely not ours ... to make sure that when they come back they cannot do any harm," Hollande told reporters.
The message "to these jihadists is that we will fight them, we will fight them and we will fight them", he said.
Hollande has said previously the attack was motivated by anti-Semitism.
A spokeswoman for the Belgian federal prosecutor's office confirmed a suspect had been arrested in Marseille but declined to give further details. Prosecutors scheduled a news conference in Brussels for 3 p.m. (1400 BST).
"This is a relief," Joel Rubinfeld, head of the Belgian League against Anti-semitism, told BFM TV.
"But this is also worrying us ... it is crucial that countries who have citizens who have gone to Syria take all necessary measures to make sure this does not happen again."
Police released a 30-second video clip from the museum's security cameras showing a man wearing a dark cap, sunglasses and a blue jacket enter the building, take a rifle out of a bag and shoot into a room before calmly walking out.
Belgian officials have said the shooting was probably a terrorist attack. Some security experts suggested it may have been the work of a hitman rather than an anti-Semitic "lone wolf".
One of the Israeli victims, Emmanuel Riva, had previously worked for Nativ, a government agency that played a covert role in Jewish migration from the former Soviet Union, an Israeli official said.
Miriam Riva, his wife, had also worked in the past for the prime minister's office, the official said.
(Reporting by Nicolas Bertin; Writing by Ingrid Melander; Editing by Andrew Roche)