Belgian police arrested seven people in overnight raids in their investigation into ISIS suicide bombings in Brussels, while authorities in France said they thwarted a militant plot there "that was at an advanced stage."
The federal prosecutor's office said six persons were held during searches in the Brussels neighborhoods of Schaerbeek in the north and Jette in the west, as well as in the center of the Belgian capital. Public broadcaster RTBF said a seventh man was arrested in the Forest borough of Brussels early on Friday.
ISIS suicide bombers hit Brussels airport and a metro train on Tuesday, killing at least 31 people and wounding some 270 in the worst such attack in Belgian history.
The daily De Standaard said on Friday police had arrested a man who was filmed by security cameras in the airport terminal next to two bombers who blew themselves up there. Prosecutors did not confirm the arrest and it was not known if the man was among the seven detained overnight.
The attack in Brussels, home to the European Union and NATO, has heightened security concerns around the world and raised questions about EU states' ability to respond in an effective, coordinated way to the Islamist militant threat.
U.S Secretary of State John Kerry arrived in Brussels on Friday for talks with Belgian and European Commission leaders to offer U.S. assistance in security cooperation against terrorism.
The Islamic State militant group also took credit for coordinated attacks in Paris in November that killed 130 people at cafes, a sports stadium and concert hall.
In Paris on Thursday, authorities arrested a French national suspected of belonging to a militant network planning an attack in France. Interior Minister Bernard Cazeneuve said in a televised address that the arrest helped "foil a plot in France that was at an advanced stage".
Cazeneuve added that the man arrested "is suspected of high-level involvement in this plan. He was part of a terrorist network that planned to strike France."
A French Interior Ministry wanted notice published by French media named him as Reda Kriket and said he was urgently sought on suspicion of terrorist conspiracy, warning he was armed and dangerous. Kriket, 34, was sentenced in absentia to 10 years in prison in Belgium last July for recruiting Islamist fighters for Syria.
After the arrest by the French counterterrorism service, DGSI, the agency raided an apartment building in the northern Paris suburb of Argenteuil. A police source said investigators found acetone peroxide explosives in the apartment.
"At this stage, there is no tangible evidence that links this plot to the attacks in Paris and Brussels," added Cazeneuve, who was in the Belgian capital on Thursday for an emergency meeting of EU interior and justice ministers.
Belgium's interior and justice ministers offered to resign on Thursday over a failure to track an ISIS militant expelled by Turkey as a suspected fighter and who blew himself up at Brussels Airport.
Brahim El Bakraoui was one of three identified suspected suicide bombers who hit the airport and metro train. 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 center.
Interior Minister Jan Jambon and Justice Minister Koen Geens tendered their resignations to Prime Minister Charles Michel, who asked them to stay on. "In time of war, you cannot leave the field," said Jambon, a right-wing Flemish nationalist.
Turkish President Tayyip Erdogan said Brahim El Bakraoui, 29, had been expelled in July after being arrested near the Syrian border and two officials said he had been deported a second time. Belgian and Dutch police had been notified of Turkish suspicions that he was a foreign fighter trying to reach Syria.
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."
Geens said systems should be reviewed but noted that other countries had been targeted, citing the Sept. 11, 2001 attacks on the United States in which he noted that "there were 3,000 dead."
Investigators are convinced the same Islamist jihadist network was involved in the November Paris attacks.
Belgian public broadcaster VRT said investigators believed that Paris attacks suspect Salah Abdeslam, arrested last Friday, probably planned a similar shooting and suicide bomb attack in Brussels. The news website Politico Europe said investigators had only questioned Abdeslam for a single hour in the four days between his arrest on March 19 and the Brussels bombings.
Belgian daily De Morgen said investigators had identified a new suspect they believe played a role in the Brussels bombings, naming him as 28-year-old Syrian Naim al-Hamed.
The paper said he was on a list circulated to the security services of other European countries after Tuesday's attacks along with Mohamed Abrini, Najim Laachraoui and Khalid El Bakraoui. Hamed was also suspected of involvement in the Paris attacks, De Morgen said.
One man was killed in a shootout with police on March 15 that led to the discovery of assault weapons and explosives and the arrest of Abdeslam, 26, and another suspect on March 18.
Belgium on Thursday lowered its security alert level one notch to three from the highest level, four, but officials did not say what that would mean in terms of security measures that have included a heavy police and military presence in Brussels.
ISIS posted a video on social media calling the Brussels blasts a victory and featuring the training of Belgian militants suspected in the Paris attacks.
The lawyer for Abdeslam said the French national wanted to "explain himself" and would no longer resist extradition to France.
Two sources familiar with the matter said the Bakraoui brothers had been on U.S. government counterterrorism watch lists before the attacks. But it was not clear how long they had been known to the authorities.
Security sources told Belgian media the other suicide bomber at the airport was Laachraoui, a veteran Belgian Islamist fighter in Syria suspected of making explosive belts for November's Paris attacks.