Belgium's capital was under the country's highest terror alert level Saturday -- with Brussels' subway service suspended and people warned to avoid gatherings -- as authorities warned of a possible imminent threat a week after deadly attacks in Paris.
Specific reasons for Friday night's alert weren't released, but as news of the heightened security measures spread, so did information about four new arrests tied to the Paris probe -- one in Brussels' Molenbeek suburb, and three in Turkey.
The Belgian Interior Ministry's crisis center cited only "a serious and imminent threat" when it announced Brussels' terror alert level was rising to 4, the country's highest. But Prime Minister Charles Michel said authorities had reason to suspect possible attacks in more than one location.
"We are talking of a threat of several individuals with weapons and explosives, to launch acts, maybe even in several places at once," Michel told reporters on Saturday.
Brussels' subway system will be closed until at least Sunday afternoon, when the threat will be reevaluated, Michel said.
