Three suspected members of Islamic State's Afghan branch ISIS-Khorasan detained in raids in Belgium were charged on Friday with planning a terrorist attack, the state prosecutor's office said.
Four other people detained during house searches across the country on Thursday were released, three of them after questioning by an investigative judge, it said.
Prosecutors said all seven taken into custody in the Brussels region and in cities including Antwerp, Liege and Ghent were natives of Chechnya, with the three who were charged suspected to be members of ISIS-Khorasan.
Prosecutors said there were no indications that the suspects had already chosen a specific target. They declined to give further information.
Belgian media had reported that investigators did not want to take any risks so close to the Olympic Games in Paris. The prosecutor's office did not respond to a Reuters' question about a possible connection to the Games, whose opening ceremony was scheduled on Friday evening.
Belgium as a hotspot for terror planning
The French anti-terrorism prosecutor told Reuters no arrest or search occurred in France as part of the investigation but did not say if French authorities were involved in it.
The perpetrators of the 2015 Paris attacks, in which 130 people were killed and 368 wounded, largely planned and coordinated them from neighboring Belgium, and several of the attackers were Belgian nationals or residents.
In 2016, bombings at Brussels airport killed 34 people and injured 340. Among those convicted for the attacks was Salah Abdeslam, who was also the main suspect in the Paris attacks trial.