Brussels central train station was evacuated for about an hour on Sunday because of a suspicious suitcase amid heightened security fears in the Belgian capital after a huge anti-terror operation led to three men being charged with terrorism offenses.
The suitcase later turned out to be a false alarm but shows Belgium's high state of alert as the Euro 2016 soccer tournament is under way in neighboring France, three months after Islamist bombers killed 32 people in Brussels.
Investigators say the attackers had links to militants who carried out attacks in Paris in November.
Belgian police searched 40 houses and 152 garage lockups between Friday night and Saturday, arresting 12 people following reports of possible attacks targeting soccer fans watching the matches in Brussels. They later released nine after questioning.
The three Belgian men charged with "having attempted to commit a terrorist murder and for participation in the activities of a terrorist group" were identified by prosecutors only as 27-year-old Samir C., 40-year-old Moustapha B., and 29-year-old Jawad B.
Belgian media reported they had links to the men prosecutors believe carried out the Brussels twin bombings in March, brothers Ibrahim ('Brahim') and Khalid El Bakraoui and Najim Laachraoui.
Without citing sources, RTBF said police listened to phone conversations between the three men in which they said they planned attacks in Brussels over the weekend.
Neither prosecutors nor Prime Minister Charles Michel confirmed reports of the arrested suspects planning to attack soccer fans.
The Belgian federal prosecutor's office said only that the investigation required immediate action.
Michel appealed to the country to stay calm after chairing a meeting of the government's security council on Saturday.
Investigators have found links between the Brussels attackers and Islamist militants who killed 130 people in a spate of shootings and suicide bombings in Paris in November.
On Friday police arrested and detained a 30-year-old man named as Youssef E.A, a Belgian national, on suspicion of taking part in terrorist activities in connection with the Brussels attacks.
The man worked at Brussels airport and had access to planes on the tarmac, said broadcaster RTBF and newspaper Le Soir, citing judiciary sources.