Belgian security forces raided an Islamist cell planning attacks against police on Friday as dozens of people were arrested in sweeps across Europe, keeping the continent on alert one week after the Paris attacks.
Two suspected jihadists were shot dead in a police raid in the eastern Belgian town of Verviers on Thursday night and prosecutors said 13 suspects had been detained across Belgium, with two more held in France.
French police separately detained 12 people in the suburbs of Paris in connection with last week's attacks on the Charlie Hebdo satirical magazine, a Jewish supermarket and a policewoman, in which 17 people died.
Hundreds of German police meanwhile raided alleged Islamist sites in Berlin, arresting two men suspected of being part of a group planning to carry out an attack in Syria.
The raids fuelled fears about the thousands of young Europeans thought to have gone to fight with the Islamic State and Al-Qaeda-linked groups in the Middle East before coming home to launch attacks.
"The group was on the verge of carrying out terrorist attacks to kill police officers on public roads and in police stations," Belgian federal prosecutors' spokesman Eric Van der Sijpt told a news conference about the raids overnight.
The group, which had recently returned from Syria, had Kalashnikov assault rifles, explosives, ammunition and communications equipment, along with police uniforms, he said.
Belgium army ready
Prime Minister Charles Michel said he was ready to call up the army to ensure security and raised Belgium's terror alert to three on a scale of four.
The European Commission stepped up security at its headquarters in Brussels as a "precaution", a spokeswoman said.
Jewish schools in Brussels and the port city of Antwerp closed Friday. The raid comes less than a year after four people were shot dead in an attack on the Jewish Museum in Brussels. A Frenchman who fought in Syria has been charged with the murders.
The unrest across Europe has fuelled fears of tensions between communities, but in Verviers, a faded industrial town near the German border, residents said they would stay united.
"The Muslim community had the strongest reaction, one that says that none of this should exacerbate the delicate balance that makes this town stand on its feet," mayor Marc Elsen said.
Belgium has one of the largest number of extremists who have returned from Syria relative to its population, with a large Muslim community that suffers from high unemployment and disenfranchisement.
With France still reeling from the attacks which targeted its cherished traditions of free speech, US Secretary of State John Kerry laid wreaths on Friday at both Charlie Hebdo offices and the Jewish supermarket during a visit to Paris.
The magazine inflamed Muslims in many countries by printing cartoons of the Prophet Mohammed.
French President Francois Hollande meanwhile urged the international community to offer a "firm" and "collective" response to the attacks, which drew 1.5 million people into the streets in Paris in their wake along with dozens of world leaders, although the US was not among them.
The funeral of Stephane Charbonnier, alias Charb, the editor-in-chief of Charlie Hebdo, was also due to take place on Friday.
The nine men and three women arrested in France overnight were to be questioned about "possible logistic support" they may have given to the gunmen -- Islamist brothers Said and Cherif Kouachi and Amedy Coulibaly -- in particular weapons and vehicles, the source said.
There was a fresh scare when a man took two hostages Friday in a post office in a Paris suburb, but he later gave himself up and there appeared to be no Islamist link.
In Germany an alleged leader of a Turkish and Russian group planning to carry out an attack in Syria and the man in charge of financing were arrested in raids on suspected Islamist sites in and around Berlin by more than 200 police officers, officials said.
International anger over Charlie Hebdo's printing of a new image of Mohammed in its sold-out comeback issue this week continued to rage, with protesters clashing with police outside the French consulate in the Pakistani port city of Karachi.
AFP photographer Asif Hassan was shot while covering the protest but appeared to be out of danger following surgery.