Greek antiterrorist police arrested four people in Athens, while in Belgium authorities used paratroopers to reinforce police in Belgian cities for the first time in three decades as European moved to counter a potential terrorism threat.
Greek authorities announced January 17 that raids in Athens resulted in four people being arrested, but reports that one of them might have been linked to a terrorist cell in Belgium turned out to be incorrect.
Belgian authorities were hopeful one of the people detained during the Athens' raids was Abdelhamid Abaaoud, a 27-year-old Brussels resident of Moroccan origin who is believed to be a leader in an Islamist terrorist cell Belgian security forces moved against on January 15.
Spokesman for the Belgian prosecutor's office Eric Van der Sypt said after checking information from Greece about the people arrested in Athens, officials in Belgium determined "those people had nothing to do with the Belgian case."
Belgium has deployed troops across the country in the wake of the January 15 raids, which Belgian authorities say were conducted to head off an "imminent terrorist attack."
Belgian officials later disclosed the raids targeted a group that was plotting to attack policemen in the country.
As of January 17, about 300 troops were deployed in the capital, Brussels, and the northern city of Anvers, which has a large Jewish population.
German police also arrested two men in Berlin suspected of recruiting fighters and supplying funds to the Islamic State (IS) militant group in Syria on January 16.
Europe has been on edge since the attack on the French satirical magazine Charlie Hebdo in Paris on January 7 and subsequent attacks in the French capital.
The attackers were seemingly motivated by anger over drawings and other insults directed at the Islamic prophet, Muhammad.
The militant group Al-Qaeda in the Arabian Peninsula took responsibility for the attacks in France, though some terrorism experts have cast doubt on that claim since it was made.
But the hundreds of citizens of European countries who have gone to Syria and Iraq, many joining the IS, remain a concern for European governments who fear these citizens will return from the war zones of the Middle East to carry out attacks in Europe.