Authorities in France and Belgium conducted over 160 raids on Monday in search of suspects connected to the deadly terrorist attacks in Paris.

The Washington Post reports police arrested at least one person in the Molenbeek district of Brussels. The majority Muslim neighborhood is known to have past links to terrorist activities.

In France, nearly two dozen people were apprehended, though it is unclear if any major suspects were caught. Police have since released some of those arrested.

This widespread anti-terrorism campaign comes after the worst attacks Paris has experienced since World War II. The Islamic State extremist group took responsibility for a series of shootings and bombings in the French capital Friday, killing at least 129 people, and injuring 350 more.

Among the major suspects in the attack is 27-year-old Belgian native Abdelhamid Abaaoud. He is currently believed to be the mastermind behind the Paris attacks.

An anonymous official told The New York Times Abaaoud spoke to a French citizen while in Syria of plans to attack "a concert hall." The ISIS militant is also suspected of plotting a foiled terrorist attack against Belgium in January.

Another suspect sought in the Brussels raid was 26-year-old Salah Abdeslam, who is believed to be the gunman who escaped authorities during the Paris attacks.

People circulated images of the suspects on social media.

The Guardian reports officers searched the home of Samy Amimour in the suburban neighborhood of Drancy in Paris. The 28-year-old man killed himself in a suicide bombing at the Bataclan theater.

Aminour was a former bus driver who turned torward radical Islam sometime before his home was raided in 2012. After being placed under survellience, the future terrorist left for Syria.

"After his arrest, Samy changed," school friend Kais Benhamouda told The Guardian. "He was a different person. He gave up his job and he left home. He said he was 'tired of France', he was fed up with the country. He didn't speak much and was quite a loner. We saw him less and less."

After identifying five of the seven dead assailants, authorities concluded that the majority of attacks were French citizens.

French Interior Minister Bernard Cazeneuve declared war on ISIS on Monday.

"It is not they who will destroy the Republic," Cazeneuve said. "The Republic will destroy them."

In other news, CNBC reports the hacker group Anonymous has also declared war on the terrorist organization.

An unverified video shows an Anonymous spokesperson, wearing a Guy Fawkes mask, speaking in French to the Islamic State.

"Anonymous from all over the world will hunt you down. You should know that we will find you and we will not let you go. We will launch the biggest operation ever against you," reads a translation of the spokesperson's statement.

Watch the video below: