Belgian authorities were searching for clues early Friday after police killed two in raids aimed at jihadists returning from Syria who were planning to launch a "Belgian Charlie Hebdo" attack, officials said.

Police were searching in Verviers, where the raid took place, and the greater Brussels area as part of a weeklong investigation that started well before the terrorism spree last week that led to 17 deaths in the Paris area. The Belgian operations had no apparent link to the terrorist acts committed in France.

And, unlike the Paris terrorists, who attacked the office of a satirical newspaper and a kosher grocery store, the suspects in Belgium were reportedly aiming at hard targets: police installations.

"They were on the verge of committing important terror attacks," federal magistrate Eric Van der Sypt said at a news conference in Brussels.

"We've averted a Belgian Charlie Hebdo."

- Belgian police officer

Across Europe, anxiety has grown as the manhunt continues for potential accomplices of the three Paris terrorists, all of whom were shot dead by French police. Authorities in Belgium signaled they were ready for more trouble by raising the national terror alert level from 2 to 3, the second-highest level.

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Prime Minister Charles Michel said the increase in the threat level was "a choice for prudence."

"There is no concrete or specific knowledge of new elements of threat," he said.

The suspects in Verviers opened fire on police when they closed in on them near the city's train station, the magistrate told reporters. There was an intense firefight for several minutes. Video posted online showed a dark view of a building amid blasts, gunshots and sirens, and a fire with smoke billowing up. Two terror suspects were killed in the shootout, and another was arrested.

No police were wounded or killed in the clash, which occurred at the height of rush hour in a crowded neighborhood of this former industrial town of 56,000 about 80 miles southeast of the capital, Brussels.

Belgian news site L'Avenir, as well as Le Soir and France24, reported late Thursday that the government prosecutor's office said a dozen operations were launched against suspects across Belgium, in Verviers, Brussels and Hal-Vilvoorde. Some of those targeted are known to have returned recently from Syria.

The Belgian news site reported that, based on phone intercepts in the homes and cars of the three individuals involved in a shootout in Verviers, authorities believed the three were in the process of carrying out imminent attacks inside Belgium.

The French daily Le Soir is reporting that the investigations were launched against the Verviers suspects at least two weeks ago after they returned from Syria where they were thought to be involved in the fighting there.

The raids earlier Thursday included one on an apartment above a bakery in the eastern city of Verviers, authorities said. Authorities said the terror cell had ties to ISIS and was planning a major attack.

"We've averted a Belgian Charlie Hebdo," an unidentified police officer told La Meuse.

Earlier Thursday, Belgian authorities said they were looking into possible links between a man they arrested in the southern city of Charleroi for illegal trade in weapons and Amedy Coulibaly, who killed four people in a Paris kosher market last week.

The man arrested in Belgium "claims that he wanted to buy a car from the wife of Coulibaly," Van der Sypt said. "At this moment this is the only link between what happened in Paris."

Van der Sypt said that "of course, naturally" we are continuing the investigation.

At first, the man came to police himself claiming there had been contact with Coulibaly's common-law wife regarding the car, but he was arrested following a search of his premises when indications of illegal weapons trading were found.

A Belgian connection figured in a 2010 French criminal investigation into a foiled terrorist plot in which Coulibaly was one of the convicted co-conspirators. The plotters included a Brussels-area contact who was supposed to furnish both weapons and ammunition, according to French judicial documents obtained by The Associated Press.

Several other countries are also involved in the hunt for possible accomplices to Coulibaly and the other gunmen in the French attacks, brothers Cherif and Said Kouachi.

In Spain, authorities said Coulibaly drove his common-law wife from France to Madrid on Dec. 31 and was with her until she took a Jan. 2 flight to Istanbul.

Spain's National Court said in a statement it was investigating what Coulibaly did in the country's capital with his wife, Hayat Boumeddiene, and a third person who wasn't identified but is suspected of helping Boumeddiene get from Turkey to Syria.

France is on edge since last week's attacks, which began at the satirical newspaper Charlie Hebdo. The paper, repeatedly threatened for its caricatures of the Muslim Prophet Muhammad, buried several of its slain staff members Thursday even as it reprinted another weekly issue with Muhammad on its cover.

Also, defense officials said France was under an unprecedented cyber assault with 19,000 cyberattacks launched after the country's bloodiest terrorist attacks in decades, frustrating authorities as they try to thwart repeat violence.

Around 120,000 security forces are deployed to prevent future attacks.

Calling it an unprecedented surge, Adm. Arnaud Coustilliere, head of cyberdefense for the French military, said about 19,000 French websites had faced cyberattacks in recent days, some carried out by well-known Islamic hacker groups.

The attacks, mostly relatively minor denial-of-service attacks, hit sites as varied as military regiments to pizza shops but none appeared to have caused serious damage, he said. Military authorities launched round-the-clock surveillance to protect the government sites still coming under attack.

The Kouachi brothers claimed allegiance to Al Qaeda in Yemen, and Coulibaly to the Islamic State group.

The Associated Press contributed to this report.