Belgium has begun deploying hundreds of troops to guard potential targets of attacks, including Jewish sites and diplomatic missions, following a series of raids and arrests, the government said.
Up to 300 soldiers will be gradually deployed in the capital Brussels and the northern city of Antwerp, which has a large Jewish population, Prime Minister Charles Michel's office said in a statement on Saturday.
The soldiers could also eventually be deployed to the industrial eastern city of Verviers, where early on Friday security forces killed two suspected attackers in a huge raid on an alleged "terror cell" planning to attack police in the country.
"The mobilised troops will be armed and their primary responsibility will be to survey certain sites" and to reinforce police, the prime minister's statement said.
The soldiers will initially be stationed at locations such as the US and Israeli embassies in Brussels and NATO and European Union institutions.
The Belgian raid came a week after attacks in and around Paris killed 17 people, rekindling fears in Europe about the threat posed by young Europeans returning home after fighting in the Middle East.
Troops will reinforce police ranks until at least Thursday, when authorities will review the national threat level, set at 3 on a scale of 4 this week, Belgium Defence Minister Steven Vandeput said on Saturday.
"It's very important to say that this wasn't a simple decision. But it was necessary, at a time when police are overly engaged, for the army to enter in a supporting role," he said.
Meanwhile, Greek police said at least four people were arrested in Athens on Saturday.
A day later, prosecutors said no link had been established between those suspects and the cell broken up this week in Belgium,.
A Greek police source said investigators had sent DNA evidence and fingerprints to Belgium to establish whether Abdelhamid Abaaoud, the 27-year-old suspected mastermind of the Belgian cell, was among the four suspects.
Following the raid in Verviers, Belgian police arrested 13 people during a series of raids across Belgium, five of whom were later charged with "participating in the activities of a terrorist group".
Belgian prosecutors said there were no immediate links with last week's attacks in Paris on the Charlie Hebdo satirical newspaper, a Jewish supermarket and a policewoman, the country's worst attacks in half a century.