The attacks came days after the arrest of November 13 Paris attacks suspect Salah Abdeslam in Brussels.
Belgian Justice Minister Koen Geens said on Friday that Abdeslam, who had initially agreed to co-operate with investigators, had ceased to do so.
"The federal prosecutor has just informed me that Salah Abdeslam no longer wants to talk since the attacks on Zaventem (airport) and the Brussels metro," he said.
Also it emerged that police in Mechelen had failed to pass on vital information in December 2015 to colleagues in Brussels that could have led them to Abdeslam.
Local police chief Yves Bogaerts said that the information was not deliberately withheld.
The Islamic State has said that it carried out both the Brussels and Paris attacks. Brussels attack left more than 30 people killed while at least 130 people were killed in the Paris attacks.
As clear connections emerged between the militants involved in the two sets of attacks, French President Francois Hollande warned of a threat from other similar networks.
"We have had success in finding the terrorists both in Brussels and in Paris," he said.
"There have been some arrests, and we know there are other networks, because even though the one that carried out the attacks in Paris and Brussels is in the process of being wiped out with a number of its members arrested, there's still a threat looming."
Brahim el-Bakraoui has already been named as one of the perpetrators of the airport attack. A third person remains unidentified.
In the same statement, the prosecutor's office said that three more arrests were made in Brussels on Friday.
Turkey has said it arrested and deported Brahim el-Bakraoui, last June, warning Belgium he was a "foreign fighter" — but the message was "ignored".
Bakraoui's brother, Khalid, attacked Maelbeek metro station, where at least 20 people were killed.
Business Standard has always strived hard to provide up-to-date information and commentary on developments that are of interest to you and have wider political and economic implications for the country and the world. Your encouragement and constant feedback on how to improve our offering have only made our resolve and commitment to these ideals stronger. Even during these difficult times arising out of Covid-19, we continue to remain committed to keeping you informed and updated with credible news, authoritative views and incisive commentary on topical issues of relevance.
We, however, have a request.
As we battle the economic impact of the pandemic, we need your support even more, so that we can continue to offer you more quality content. Our subscription model has seen an encouraging response from many of you, who have subscribed to our online content. More subscription to our online content can only help us achieve the goals of offering you even better and more relevant content. We believe in free, fair and credible journalism. Your support through more subscriptions can help us practise the journalism to which we are committed.
Support quality journalism and subscribe to Business Standard.