(CNN) The four men killed by terrorists in a kosher supermarket in Paris last week now rest in Jerusalem, 2,000 miles away from the country they called home and where images from a massive rally Sunday inspired France -- and the world.

At that demonstration, some Muslims held signs that not only echoed the rallying cry "Je Suis Charlie" but also proclaimed "Je Suis Juif" ("I Am Jewish"). The public overture was especially poignant at a time when the two communities are so often pitted against one another.

But on the same day that brought this and other messages of hope, the Jewish Agency for Israel reported that hundreds of French Jews attended an information fair in Paris, held under tight security, to explore immigration to Israel. Though the event had been scheduled before last week's terror attacks, the turnout suggested that for some French Jews this unity rally may have come too late.

Numbering about a half-million, the Jewish community in France is the largest in Europe -- and third largest in the world after Israel and the United States. Rising anti-Semitism in recent years, however, has chipped away at the numbers.

Seven thousand French Jews moved to Israel in 2014, according to the Jewish Agency. That number more than doubled the previous year's figure, and for the first time more Jews moved to Israel from France than they did from any other country.

A year marred by anti-Semitism

The attack on the kosher market Friday came during a manhunt for suspects in the killing of 12 at the satirical French magazine Charlie Hebdo two days earlier. Four died in the market, making it the deadliest attack on French Jews in nearly three years. In March 2012, a teacher and three students were gunned down at a Jewish school in Toulouse

Before the Friday siege at the market even ended, Jewish businesses in the area were shuttered and Paris' largest synagogue, the Grande Synagogue, was closed for Shabbat services for the first time since World War II.

The violence came after a year marred by unsettling developments in France, a sampling of them listed by Tablet , an online Jewish magazine.

Among the anti-Semitic incidents were reports of Jewish teens, who wore traditional Jewish items like yarmulkes, being assaulted with Tasers, tear gas and pepper spray. A Jewish teacher leaving a kosher restaurant in Paris was attacked, his nose broken and a swastika drawn on his chest. Two teens and their grandfather were chased by a group, including a man wielding an ax, as they walked to synagogue in Paris.

Two French teenage girls plotted to blow up a synagogue in Lyon. A kosher restaurant in Paris was firebombed. A kosher supermarket was set ablaze in Sarcelles. A man shook a mother's baby carriage at a bus stop in Paris and said to her, "Dirty Jewess, enough with your children already."

Between January and the end of July of 2014, the most recent data available, there were about 620 anti-Semitic incidents in France, a 91% increase over the year before, said Simone Rodan-Benzaquen, the Paris director of the American Jewish Committee, a global Jewish advocacy agency. The sad reality, she added, is that most of these anti-Semitic acts were committed by "disenfranchised Muslims."

But this uptick is the result of two simultaneous developments in France, said Bobby Ghosh, a global affairs analyst for CNN. In conversation with CNN's Jim Sciutto , Ghosh pointed to the "rise of the extreme right" political party of Marine Le Pen, "which is openly xenophobic," and to the "rise of Islamic radicalism." (In May, Le Pen's Front National finished first among all parties in France's European Parliament elections, winning a quarter of the vote).

Flames of hatred were further fueled by Israel's operation in Gaza over the summer. Anti-Israel demonstrations morphed into a new level of ugliness.

About 400 Jews gathered in July to pray for peace at Paris' Don Isaac Abravanel Synagogue. They found themselves trapped inside for hours as demonstrators screamed, "Death to the Jews," a witness outside the synagogue told CNN . Some of the Jews inside heard cries of "Jews to the oven" and saw men brandishing knives and broken bottles.

"The level of danger is very new," Serge Benhaim, the synagogue president who was inside that day, told CNN afterward. "Today and tomorrow for the Jewish people in France is fully different from what it was yesterday."

That was half a year ago. What lies ahead may look even more different.

Threats to Jewish columnist at magazine

Last week's three-day siege by Islamist terrorists left 17 dead in and around Paris. A policewoman was killed after the attack at the offices of Charlie Hebdo. The killings at the kosher market came as Jews shopped in preparation for Shabbat.

And while the last attack was deemed obviously anti-Semitic, one death at Charlie Hebdo may have been, too.

On Friday, CNN's Erin Burnett spoke to Sophie Bramly, the cousin of Elsa Cayat, the only woman killed at the magazine. Other women were specifically told by the attackers that they would be spared because they were women, and Bramly believes Cayat was not because she was Jewish.

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Bramly had spoken to Cayat's brother the night before and learned that Cayat, a psychoanalyst and columnist, had been receiving anonymous phone calls. They included threats like, "Dirty Jew, you should stop working for Charlie Hebdo. Otherwise we're going to kill you," she told Burnett.

"The press hasn't really talked about it that way here. It was only about freedom of speech that was attacked and my feeling was that religion was there, too," she said. "And today [the kosher market siege], unfortunately, seemed to prove that I wasn't totally wrong."

Perhaps if France had acted more forcefully when only Jews were the targets of Islamist violence, this never would have happened, some said on social media. Others debated if there was a future for Jews in France. Some invoked the famous Nazi-defying quotation of German Lutheran pastor Martin Niemöller in sentiments such as, "First they came for the Jews, but I did not speak out because I wasn't a Jew. Then they came for the journalists."

Conspiracy theories blaming Jews and Israel for the Charlie Hebdo attack that killed Bramly's cousin are already making the rounds, the Anti-Defamation League reported

The organization listed a flurry of accusations being made in the U.S. and abroad, a number of them pointing fingers at the Israeli intelligence agency Mossad. The Tunisia Times, the ADL said, ran an article Friday that read, "the Mossad hired Muslims from Arabic origins to carry the attack to increase hostility towards Muslims worldwide."

'A massive exodus'

By Sunday morning, a makeshift memorial outside the kosher market drew crowds. Members of the Jewish community prayed, and others came declaring "Je Suis Juif" to show support.

Also on hand and shaking hands with Parisian Jews was Naftali Bennett, the controversial right-wing leader of the Jewish Home Party in Israel, CNN's Atika Shubert reported. Like other Israeli politicians in recent days, including Prime Minister Benjamin Netanyahu, he shared the message that Israel is home to any Jews who want to move there.

JUST WATCHED French Jewish communities unsettled by attack Replay More Videos ... MUST WATCH French Jewish communities unsettled by attack 02:41

"If they decide to come to Israel, we will accept them and embrace them," he said. "If they decide to stay here, we will continue to make sure they're secure. The world has to wake up."

Several people in the crowd told CNN they planned to leave. "The Jewish community is no longer safe," said one man. "I will leave for Israel," a young woman said, "because unfortunately now, here, I'm afraid."

Later on Sunday, after the unity rally, the Grande Synagogue filled for a memorial service.

Seated two rows behind Israel's Prime Minister was Soviet-born Natan (formerly Anatoly) Sharansky, who was sentenced in 1977 to forced labor in a Siberian prison camp, or gulag. What landed him there for nine years was his human rights activism and insistence on making aliyah, or moving to Israel.

Today the Israeli politician, activist and author -- his books include "Fear No Evil," "The Case for Democracy," and "Defending Identity" -- is the chairman of the Jewish Agency.

While 7,000 French Jews made aliyah in 2014, he recently told The Jerusalem Post that 50,000 had inquired about it. And while a year ago information seminars about immigration to Israel were held once a month in France, he said they are now held twice a day.

"Here you have for the first time, a clear thing," Sharansky told the newspaper. "There is a massive exodus from a community in the free world, which has all the doors open to them, and they are choosing Israel."

Evidence of French Jews moving to Israel can be seen in Ashdod, a seaside community where an art center is modeled after the Louvre and conversations at cafes are more likely to be in French than Hebrew, reported CNN's Ian Lee

High-rise apartment buildings are under construction in Ashdod and a developer told Lee that since August the majority of buyers have come from France.

A woman named Catherine, who only wanted to use her first name, arrived two weeks ago. She told Lee that friends and family would soon follow.

"The [French] government, they say to us, 'We don't want you to go,'" she said, in broken English. "But they don't do nothing that makes us stay."

'They love this country and want to stay'

The bulk of Jews in France, however, are not ready to give up on their country, said Noam Meghira, vice president of the French Union of Jewish Students.

"Some people want to leave. This is their choice," Meghira told CNN's Jim Sciutto. "But this is a minority. The majority of French Jews are in France. ... They love this country, and they want to stay here."

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It's why they, too, rallied in solidarity with the masses on Sunday. They'd like to remember how a Muslim employee at the kosher supermarket helped saved Jews. They know a threat to them is also a threat to democracy. They point to beefed-up security as evidence of how seriously their home country is looking out for them.

About 4,700 officers have been tasked with securing 717 Jewish schools, French Prime Minister Manuel Valls told CNN affiliate BFMTV.

Valls doesn't want Jews to leave. France, he's even said, depends on their staying.

"The choice was made by the French Revolution in 1789 to recognize Jews as full citizens," Valls told The Atlantic's Jeffrey Goldberg before last week. "To understand what the idea of the republic is about, you have to understand the central role played by the emancipation of the Jews. It is a founding principle."

So if Jews were to leave en masse, the French Republic would be "judged a failure," he said.

"If 100,000 French people of Spanish origin were to leave, I would never say that France is not France anymore," said Valls, whom Goldberg noted is the son of Spanish immigrants. "But if 100,000 Jews leave, France will no longer be France."

While some people have left, and perhaps more will, Rodan-Benzaquen, the Paris AJC director, is not fretting about a "mass exodus," which she called overstated. She'd rather wait to see if France will do everything it can to make Jews feel safe.

"I'm more worried about the state of mind of people who are in France and asking themselves if they have a future here," she told CNN by phone late Monday. "It affects the way they live in this country."

If they feel lonely or disconnected from France, that would signal trouble.

"Jews are totally intertwined with what the French Republic is about," she said. "French Jews are French, and they want to continue living in the country."

In fact, when Jews go to synagogue, she said, they offer up a special prayer. It is a prayer for the republic, the place that for centuries has been their home.