Belgian officials have named the second suicide bomber in Tuesday's attack at Brussels airport as Najim Laachraoui, and said that his DNA was found at sites of the November Paris attacks.
The news came as three people were arrested in Brussels in connection with the attacks.
Prosecutors said the arrests were linked to a raid in Paris on Thursday, where an attack was apparently foiled.
Other suspects have been arrested in Belgium, Germany and France.
Thirty-one people died in bombings at Brussels airport and a metro station.
The attacks came days after the arrest of 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 in parliament.
Also it emerged that police in Mechelen, north of Brussels, 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 the information was not deliberately withheld.
So-called Islamic State (IS) has said it carried out both the Brussels and Paris attacks.
On Friday it released a video about the Brussels attacks, presenting them as retribution for coalition attacks against IS territory in Iraq and Syria.
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."
What Belgian prosecutors said about Laachraoui:
Left DNA on a piece of cloth at the Bataclan and on an explosive device at the Stade de France in November
DNA also found in a flat in Brussels and a house in Auvelais in southern Belgium, both used by the Paris bombers