Belgium on Saturday began deploying scores of troops to patrol the streets after security forces smashed a suspected Islamist terrorist cell planning to kill police officers.
Some 150 soldiers took up positions in the northern town of Antwerp, notably to protect diamond jewelers and a large concentration of Orthodox Jews.
The NATO headquarters, various EU offices and the US and Israeli embassies are also in the area, as well as Brussels' main synagogue, said Defense Minister Steven Vandeput.
Antwerp has a large Jewish population.
"The mobilized troops will be armed and their primary responsibility will be to survey certain sites" and to reinforce police, Prime Minister Charles Michel's office said in a statement.
Outside the Jewish Museum of Brussels, where a jihadist terrorist killed four people in May 2014, armed soldiers stood watch.
Up to 300 troops may be deployed in the biggest operation since the terrorist bombings carried out by the Communist Combatant Cells of the mid-1980s.
Soldiers have also been requested at the industrial eastern city of Verviers, where early on Friday security forces killed two suspected Islamist terrorists in a huge raid on an alleged jihadist cell allegedly planning to attack police in the country.
The Belgian raid came a week after Islamist attacks in and around Paris killed 17 people, rekindling fears in Europe about the threat posed by young Europeans returning home after fighting alongside extremist groups in the Middle East.
Following the raid in Verviers, Belgian police arrested 13 people across Belgium, five of whom were later charged with "participating in the activities of a terrorist group."
Weapons, bomb-making materials, police uniforms and fake documents were found during searches of their homes.
Belgian prosecutors said there were no immediate links with last week's Islamist attacks in Paris on the Charlie Hebdo satirical magazine, a Jewish supermarket and a policewoman, the country's worst attacks in half a century.
Two fugitives who left Belgium immediately after the attack have been arrested in the French Alps.
The suspected mastermind of the cell, Abdelhamid Abaaoud, is a notorious 27-year-old jihadist who spent time in Syria and who may have prepared the foiled attack from bases in Greece and Turkey, according to local media.
'Possible logistical support'
French and Belgian authorities were grilling suspected accomplices both of the Paris gunmen and the alleged terrorist cell raided in eastern Belgium.
French police separately arrested 12 people early Friday and questioned them about "possible logistical support" they may have given to the Paris gunmen - Islamist brothers Said and Cherif Kouachi and Amedy Coulibaly, sources said.
The raid came less than a year after four people were shot dead in an attack on the Jewish Museum in Brussels. A Frenchman who fought alongside ISIS in Syria has been charged with those murders.
With France still reeling from the attacks that targeted its cherished traditions of free speech, US Secretary of State John Kerry laid wreaths on Friday at both the Charlie Hebdo offices and the Jewish supermarket during a visit to Paris.
The United States condemned the violence, saying there was a "universal" right of the press to freely publish any kind of information, including caricatures.
In Washington, US President Barack Obama and British Prime Minister David Cameron vowed to help France and others defeat global terrorism with stronger cooperation and surveillance.
In London, authorities were mulling "further measures" to protect police "given some of the deliberate targeting of the police we have seen in a number of countries across Europe and the world," said Mark Rowley, head of counter-terrorism for the British police.
British Prime Minister David Cameron has also ordered increased security for areas with large Jewish communities.
AFP contributed to this report.