Four men accused of having links to the jihadists behind the Paris attacks were due to appear before a judge in France on Tuesday, while police in neighboring Germany staged fresh raids on suspected extremists.
The four men, aged between 22 and 28, were arrested on Friday on suspicion of helping supply weapons and vehicles to the gunmen who killed 17 people in three days of violence around Paris.
Four other men and four women -- aged between 19 and 47 -- were also arrested last week but have been released without charge.
With Europe on high alert, some 200 German police raided more than a dozen apartments, hunting a jihadist network they believe was planning an attack in Syria.
Police said they searched 13 apartments in Berlin, a neighboring region and in the east but made no arrests.
They were targeting people linked to the alleged leader and financier of the group who were detained after raids in Berlin on Friday.
Tensions have been mounting across Europe in the wake of the Paris attacks and a raid in Belgium last week that broke up another suspected plot to kill police officers.
The Danish wing of Germany's anti-Islamic PEGIDA movement staged its first rallies on Monday, drawing several hundred people in the capital and other cities.
However, they were outnumbered by counter-demonstrators. In Germany, too, more than 17,000 anti-racism demonstrators took to the streets across the country on Monday in opposition to PEGIDA, which had been forced to cancel its own rally following a terrorist threat.
Muslim 'hero' naturalized
Meanwhile, the Muslim employee who has been hailed as a hero for helping customers in the Jewish supermarket where four people were killed during the Paris attacks, was due to be granted French citizenship.
Some 273,000 people signed a petition calling for Lassana Bathily, 24, from Mali to be naturalized after he tried to hide customers in the cold storage room.
Police officers stand along the road as the hearse carrying the coffin of French municipal police officer from Martinique Clarissa Jean-Philippe, who died in an attack in Montrouge, south of Paris on January 8, drives in a procession during her funeral in Sainte-Marie, on the French Caribbean island of Martinique, on January 19, 2015. Photo: AFP
President Francois Hollande insisted his country "insults no-one when we defend our ideas, when we proclaim freedom".
But Prime Minister Manuel Valls acknowledged that France suffered "social and ethnic apartheid" as a result of the sharp inequalities faced by many immigrant and poorer families.
"'Je suis Charlie' is not our only message to the world," he said in a speech on Tuesday, referring to the slogan that went viral after the deadly attacks on the satirical magazine Charlie Hebdo on January 7.
"France carries freedom of expression everywhere, but it also defends other values it holds dear: peace, respect for beliefs, dialogue between religions."
Valls was apparently responding to a wave of giant protests across several parts of the Muslim world against Charlie Hebdo, the main target of the Paris attacks for its publication of cartoons of the Prophet Mohammed.
'No one goes unpunished'
After the murder of eight of its journalists by the jihadists, the magazine responded last week with another cartoon of the prophet, crying, under the headline "All is forgiven".
Several hundred thousand people flooded into the centre of Grozny, the capital of the predominantly Muslim Russian province of Chechnya, for a mammoth state-sponsored demonstration on Monday against the latest cartoon.
Authorities in the tightly controlled region said more than one million people -- almost the entire population of the republic -- took part.
"We say firmly that we will never allow anyone to go unpunished for insulting the name of the prophet and our religion," said Ramzan Kadyrov, who has ruled Chechnya with an iron fist since being installed by Russian President Vladimir Putin a decade ago.
Elsewhere, hundreds of people in Afghanistan and Pakistan demonstrated against Charlie Hebdo on Monday, burning French flags and calling for the government to cut diplomatic relations with France.
In neighboring Pakistan, five protests were held in the northwestern city of Peshawar and one in the southern port city of Karachi.
In Gaza, around 200 radical Islamists -- brandishing black jihadist banners -- threatened attacks against France.
"French, leave Gaza or we will slaughter you," the crowd chanted outside the French cultural centre.
More than 2,000 Iranians protested outside the French embassy in Tehran, chanting "Death to France", with female protesters segregated from the males.
Niger meanwhile declared three days of mourning from Monday after violent protests over the cartoons left 10 people dead and dozens of churches torched.