The chief suspect in the Paris attacks, Salah Abdeslam, was summoned to court in Brussels on Thursday morning after his arrest last week in the Belgian capital. His lawyer said Abdeslam is not fighting extradition to France, which wants him to face potential terrorism charges.
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The Islamic State group claimed responsibility for the attacks in Brussels and Paris, which have laid bare European security failings and prompted calls for better intelligence cooperation and a tougher response to Islamic State extremists.
Belgian prosecutors have said at least four people were involved in Tuesday's attacks on the Brussels airport and a subway train, including brothers Ibrahim and Khalid El Bakraoui, identified as suicide bombers. European security officials identified another suicide bomber as Najim Laachraoui, a suspected bombmaker for the Paris attacks.
Prosecutors have said another suspected participant in the airport attack is at large, a man in a hat seen in surveillance images.
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Belgian state broadcaster RTBF and France's Le Monde and BFM television reported Thursday that a fifth attacker may also be at large: a man filmed by surveillance cameras in the Brussels metro on Tuesday carrying a large bag alongside Khalid El Bakraoui. RTBF said it is not clear whether that man was killed in the attack.
Prosecutors, who have not said how many people overall may have taken part in the bombings, did not immediately respond to the reports.
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Attention turned Thursday to Paris attacks suspect Abdeslam, who evaded police in two countries for four months before Friday's capture in the Molenbeek neighborhood where he grew up. He was shot in the leg during the arrest.
The Belgian federal prosecutor's office said Abdeslam and two other suspected accomplices appeared in court Thursday.
Abdeslam's lawyer, Sven Mary, told reporters at the courthouse that he asked for a one-month delay on any transfer while he studies the large dossier, but that Abdeslam "wants to leave for France as quickly as possible."
A helicopter circled overhead, and the area was under extraordinarily heavy security, as are many parts of the Belgian capital.
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France is seeking Abdeslam's extradition to face potential terrorism charges for his involvement in the Nov. 13 attacks on a Paris rock concert, stadium and cafes, which killed 130 people. Several attackers were also killed.
Abdeslam, 26, a French citizen who grew up in Brussels' heavily immigrant Molenbeek neighborhood, slipped through police fingers on multiple occasions, including the day after the attacks.
Evidence is mounting that the extremists may have launched this week's attacks in Brussels in haste because they feared authorities were closing in on them after Abdeslam's arrest.
Later Thursday, European Union justice and interior ministers are holding an emergency meeting prompted by the Brussels attacks.
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Turkish President Recep Tayyip Erdogan said on Wednesday that Ibrahim El Bakraoui was caught in June 2015 near Turkey's border with Syria and deported, at his own request, to the Netherlands, with Ankara warning Dutch and Belgian officials that he was a "foreign terrorist fighter." But other Turkish officials said he was released from Dutch custody due to lack of evidence of involvement in extremism.
Belgium is holding three days of national mourning after the attacks on the EU capital. Security remains tight, but barriers were removed around the subway station hit by the attack, Maelbeek. The airport will remain closed until at least Saturday.
Many of the dead remained unidentified, partly because of the severity of devastation caused by the nail-packed bombs detonated in crowds. Eleven people were confirmed dead at the airport, 20 inside the Maelbeek subway station.
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