Belgian authorities arrested three more suspects, Germany arrested two and France captured one on Friday in the course of investigations into Tuesday's bombings by DAESH in Brussels.
Nine people in total were arrested since Thursday in Belgium as European authorities have swooped on militants they link both to the Brussels attacks that killed 31 people and to attacks in Paris last November that killed 130.
Germany's Der Spiegel magazine said German police had arrested two people. One had received phone messages with the name of the metro station bomber and the word "fin" - French for "end" - three minutes before the metro blast, it said. The German Interior Ministry declined immediate comment.
Three men have been arrested in Brussels over links to a French terror plot foiled by police outside Paris late on Thursday, the Belgian federal prosecutor said.
"Police carried out two searches as part of a terrorism case linked to the arrest (near Paris) of Reda Kriket," the prosecutor said in a statement on Friday.
Two of the men were injured in the leg during separate operations, the prosecutor said, the first in the Brussels district of Forest where a previous raid led to the arrest of top Paris attacks suspect Salah Abdeslam.
Kriket (34) was caught with heavy weapons and explosives in his apartment near Paris.
Kriket was sentenced in absentia by a Belgian court in February for his connection to a terror network in Brussels.
Two terror attacks hit the Zaventem Airport and another targeted Maelbeek metro station on Tuesday in Belgian capital Brussels, killing 31 people and wounding some 270 in the worst such attack in Belgian history.
The attacks were claimed by the DAESH terrorist organisation.
Turkish President Recep Tayyip Erdogan said on Wednesday that one of the attackers in the Brussels suicide bombings -Ibrahim el Bakraoui- was deported last June from Turkey, and subsequently Belgium was warned that he was a terrorist.
Earlier on Thursday, Belgium's interior and justice ministers offered to resign over their failure to track the DAESH terrorist expelled by Turkey last year who took part in a suicide attack at Brussels airport on Tuesday.
Prime Minister Charles Michel asked them to stay on.
"In time of war, you cannot leave the field," said Belgian Interior Minister Jan Jambon, a right-wing Flemish nationalist.
Ibrahim El Bakraoui was one of three identified suspected suicide bombers who hit the airport and metro train. At least one other man seen with them on airport security cameras is on the run and a fifth suspected bomber filmed in the metro attack may be dead or alive.
Bakraoui's brother Khalid, 26, killed about 20 people at Maelbeek metro station in the city centre. De Morgen newspaper said he had violated the terms of his parole in May by maintaining contacts with past criminal associates, but a Belgian magistrate had released him.
At the time, Belgian authorities replied that Bakraoui, who had skipped parole after serving less than half of a nine-year sentence for armed robbery, was a criminal but not a militant.
"You can ask how it came about that someone was let out so early and that we missed the chance to seize him when he was in Turkey. I understand the questions," Jambon said.
"In the circumstances, it was right to take political responsibility and I offered my resignation to the prime minister."
Brussels is the headquarters of both NATO and the European Union.