Since the attack in the Belgian capital on May 24, 2014, Jews have been slain in jihadist attacks in Paris and Copenhagen. Jews were also murdered in a similar attack in the French city of Toulouse in 2012.
"The threat of jihadist attacks in Europe is not limited to the Jewish community," European Jewish Congress chief Moshe Kantor told AFP.
"Islamist extremists see European democracy and freedom as their primary enemy. However, Jews remain on the frontlines," he added.
Like EU and European government officials, Kantor voiced concern that Islamist militants trained in weapons use and hardened in battle would mount more attacks in Europe following their return from Middle East war zones.
Several thousand European nationals are feared to have joined jihadist groups in Syria and Iraq.
The four people killed in the Brussels attack were Israeli couple Emanuel and Miriam Riva, French volunteer Dominique Sabrier and museum receptionist Alexandre Sterns.
Six days after the Brussels attack, police in the southern French port city of Marseille arrested 29-year-old Frenchman Mehdi Nemmouche, who had gone to fight with jihadists in Syria.
Found with weapons similar to those seen on museum security cameras, Nemmouche was extradited to Belgium at the end of July.
While waiting for his trial, for which no date has been set, he has denied having carried out the attack.
"We have had a difficult year on the personal level," said Philippe Blondin, the director of the small museum in the picturesque Sablon neighborhood of Brussels.
The time when the museum was open without security measures "has unfortunately ended," Blondin told AFP.
Visitors now walk past two well-armed Belgian soldiers and then through airport-like metal detectors to enter the building.
The museum, which reopened four months after the shooting, will exceptionally be closed on Sunday, May 24, in a sign of mourning.
But the Coordination Committee of Belgium Jewish Organizations will stage a vigil outside its doors at 3 pm (1300 GMT).
"The day of the attack, I was devastated, but I couldn't part from the feeling that it was going to happen," said Joel Rubinfeld, the president of the Belgian League Against Anti-Semitism who rushed to the scene within 30 minutes.
Rubinfeld said he has observed a rise in anti-Semitic acts in the last 15 years, but he said Jews are not the only target of the Islamists.
"What they are spreading is hatred of Jews, homosexuals, women, free-masons. In brief, those who are different," Rubinfeld told AFP.
"They are in the process of testing democracy," said Rubinfeld, who has received death threats.
He said fear is beginning to drive members of the 40,000 Jewish community to leave Belgium, adding he knows three families who will leave for Israel over the summer.
'Fear and anxiety'
Viviane Teitelbaum, a Belgian politician, said she has also been the target of insults and intimidation.
"Many Jews have started to raise questions, especially about the future of their children," Teitelbaum told AFP.
"It's sad when families leave because they no longer feel safe in the country that welcomed their parents," she added.
Israeli Prime Minister Benjamin Netanyahu invited Jews to Israel both following the February Copenhagen shooting in which an unarmed Jewish security guard was killed at a synagogue and following the January Paris attacks in which four Jews were killed at a kosher supermarket in tandem with the Charlie Hebdo attacks.
In Copenhagen, a filmmaker and security guard were killed in attacks on a cultural centre and synagogue.
European Commission First Vice President Frans Timmermans has said the EU faces a "huge challenge" to reassure Jews about their future on the continent.
Kantor said fear of anti-Semitic acts was leading to an "exodus" from Europe but he gave no figures.
"It is clear from statistics and the feeling on the ground that the situation for the Jews of Europe hasn't been as bad since the end of the Holocaust," Kantor said.
"I have never heard and felt the fear and anxiety in so many parts of Europe as I do today," he added.