More than a million people gathered Sunday in Paris after three days of terror attacks that left 17 dead. Officials said the unity march was the largest demonstration in French history.

Crowds carrying banners and placards began to assemble in central Place de la Republique in the late morning and slowly made their way toward Place de la Nation, a little under two miles away, at around 3.30pm local time. Roads into the area were packed for several hours and marchers were still moving through the starting point three hours later. Others were unable to even reach the official route and made their way across the city on neighboring streets.

Organizers said that up to 1.5 million took part in the rally, while the Ministry of the Interior described the turnout as "unprecedented," and said numbers were so high that an official count would be impossible, according to the Associated Press. The estimated turnout would make the rally the largest gathering ever in France, with more people taking to the streets than when Paris was liberated from Nazi occupation in 1944.

Photo by Etienne Rouillon

More than 40 heads of state and government from around the world arrived in France for the rally, including UK Prime Minister David Cameron, German Chancellor Angela Merkel, Spanish Prime Minister Mariano Rajoy, and Turkish Premier Ahmet Davutoglu.

Israeli Prime Minister Benjamin Netanyahu was also in attendance, and is scheduled to meet Sunday evening with French President François Hollande to discuss threats facing France's Jewish community after four of this week's victims were killed by an Islamic extremist in an attack on a kosher supermarket. Netanyahu has previously urged Jews in France and the rest of Europe to emigrate to Israel to escape hate attacks, and said before he left for Paris that any French Jew who wished to move to the country would be received "with open arms."

Photo by John Beck

Authorities said 2,000 police officers and 1,350 soldiers were deployed to protect the march attendees. Security at the event was tight, with the route completely cleared of parked vehicles Saturday night, hooded sniper teams in position on rooftops, and helicopters periodically circling above.

The terror attacks have stunned France. There is a palpable sense of shock in the capital, but demonstrators described the rally as an opportunity to express both condolences and defiance. Chants broke out regularly, as did frequent renditions of the French national anthem "La Marseillaise."

Many attendees said they wanted to stand up to terrorism, but stressed that Islam should not be conflated with extremist violence.

"It's very important to be here, this [sort of terror attack] should never happen, those are unacceptable things. I'm very optimistic because there is an awareness now," one man who gave his name as Amadou told VICE News. "People realize that fanatics are creating distress in our society. I think that people know that a religion will not commit barbarian acts, that fanatics cannot be mixed up with those who are religious."

Others voiced concerns of an increase in anti-Semitic sentiment in France.

"The rise of anti-Semitism is something that has been happening for a long time, with what [attacks] in Toulouse, in Créteil and other things that are not talked about in media," Viviane, who marched with a poster that included a Star of David, told VICE News. "One cannot assassinate people. Those were journalists, they made cartoons of rabbis, but the Jewish did not come to assassinate them. We are all equal, Muslims, Jewish, Christians."

Interior Minister Bernard Cazeneuve said after an emergency meeting Saturday that all necessary security measures would be taken, but that country would remain on the highest state of alert for weeks.

Meanwhile, police continue to hunt for accomplices of the gunmen responsible for the attacks.

The violence began Wednesday when brothers Said and Cherif Kouachi stormed the central Paris offices of satirical magazine Charlie Hebdo armed with automatic weapons. They shot 12 dead including the magazine's editor, four cartoonists, and two police officers. It was the worst terrorist act committed on French soil in decades.

The Kouachi brothers then fled the capital by car, sparking a massive manhunt that the government said involved 88,000 security personnel, including police, border agents, members of the gendarmarie, and troops. The search eventually concentrated on the Aisne region, northeast of Paris, after the two men were spotted at a gas station in the area on Thursday. They subsequently exchanged fire with police and holed up in the facilities of the Création Tendance Découverte (CTD) in an industrial zone of Dammartin-en-Goele, a commune 22 miles north of Paris.

On Friday afternoon, Amedy Coulibaly, another gunman, killed four people and held several hostages at a Hypercacher kosher supermarket in the southeastern Parisian suburb of Vincennes.

Police later killed all three men. The Kouachi brothers were gunned down when they emerged from the building firing their weapons. A civilian who had been hiding in the building emerged unharmed.

A SWAT team raided the Hypercacher, killing Coulibaly while four hostages and two police officers were wounded, according to the Associated Press. An additional 15 hostages were escorted from the scene unharmed.

Photo by Etienne Rouillon

Security forces are still hunting for Coulibaly's partner, Hayat Boumeddiene, who is reported to have been with Coulibaly when he killed a policewoman in a separate incident Thursday. Police warned that she is likely to be armed and should be considered dangerous. A number of reports have cited officials as saying that she may have travelled to Syria via Turkey.

The deaths have left France stunned and prompted outpourings of messages supporting freedom of expression and condolences from governments across the world. However, a number of the leaders in attendance at Sunday's rally come from countries which have appalling records on press freedom, including Turkey, which is consistently named the world's worst jailer of journalists, Russia, where authorities frequently harass independent journalists, and Egypt, where three Al Jazeera journalists have been jailed for over a year on charges including "falsifying news" after a widely derided trial that Amnesty International described as "a complete farce."

Additional reporting by VICE News' __Melodie Bouchaud