Bomb-damaged Brussels airport held a drill for a partial restart on Tuesday but warned it could take months to reopen fully, as under-fire Belgian authorities hunted for a suspect still on the run a week after the deadly attacks.

As Brussels struggled to get back on its feet, criticism of Belgium's handling of the case mounted after the sole suspect to be charged over the airport and metro attacks was freed for lack of evidence linking him to the carnage.

Prosecutors had charged the suspect, known as Faycal C., with "terrorist murder" and were investigating whether he was the third airport attacker who fled after his bomb did not detonate.

With his release on Monday, the hunt was back on for the so-called "man in the hat" seen in CCTV footage next to the two Islamic State suicide bombers at Zaventem airport.

The airport, closed since the blasts wrecked the departure hall, was staging a test run on Tuesday involving hundreds of volunteer staff to determine if it was ready to resume flights, albeit in a very limited capacity, from Wednesday.

A temporary check-in facility has been set up and passengers will be subject to extra security checks when it does open.

Brussels Airport chief executive Arnaud Feist also warned that even if the airport did reopen on Wednesday, it would only be at 20% capacity, handling 800-1,000 passengers an hour.

For a full return to normal, "we will have to wait for months," Feist told L'Echo daily.

Security around Zaventem was tight for the drill, with soldiers and police stopping and checking all vehicles headed for the airport.

Telephone alibi  

A total of 35 people died in the attacks at the airport and Maalbeek metro station and 340 were injured, 96 of whom remain in hospital.

Many foreign nationals were among the victims, testament to the cosmopolitan nature of a city that is home to both the European Union and Nato.

While Belgian authorities were quick to identify all three bombers, the inquiry has been dogged by accusations that Belgium missed a series of leads in cracking down on a jihadist network linked to the Brussels attacks as well as the November 13 Paris attacks that killed 130 people.

Adding to the recriminations, Brussels mayor Yvan Mayeur said he regretted the release of the man identified by Belgian media as Faycal Cheffou, who claimed to be a freelance journalist.

Hinting at suspicions that the man was a jihadist recruiter, he told French media: "There is a very thin line between an agitated radical and a radical recruiter, and in this case the judge probably didn't want to cross that line."

The man's lawyer Olivier Martins told RTBF television his client was let go because he had an alibi.

"He gave an alibi based on telephone analysis which showed that he was at home at the time of the attacks," Martins was quoted as saying.

'Enemy in Syria'  

Under pressure at home and abroad for an apparent series of missed chances in keeping tabs on criminals linked to jihadist networks, the Belgian government has admitted mistakes were made.

In the most damning revelation, Turkey accused Belgium of ignoring warnings from Ankara after it deported airport suicide bomber Ibrahim El Bakraoui as a "terrorist fighter" last year after arresting him near the Syrian border.

Two Belgian ministers, including Justice Minister Koen Geens, offered to resign last week after the Turkish link emerged.

Underscoring the tense political climate in a notoriously complex and fragmented country, Geens on Tuesday called for unity.

"This is not the time to argue with each other. As far as I know the enemy is in Syria," he told VRT television.

In a bid to uncover the identity of the mystery third airport suspect, police have released video footage of a man in a hat and white jacket pushing a trolley with a large bag through the departure hall, next to suicide bombers Ibrahim El Bakraoui and Najim Laachraoui.

Bomb-maker Laachraoui's DNA was found on some of the explosives used in Paris.

Ibrahim El Bakraoui's brother Khalid, who blew himself up on a Brussels metro train shortly after the airport blasts, is meanwhile believed to have rented a property linked to Paris prime suspect Salah Abdeslam.

Raids and arrests in Belgium, France and the Netherlands since the Brussels bombings have exposed a complex web of jihadist cells, underscoring the need for better European coordination in the fight against terrorism.

Dutch prosecutors on Tuesday said a French terror suspect arrested in weekend raids in Rotterdam intends to fight his extradition to France.

The man, identified as Anis B., was detained on Sunday suspected of receiving orders from the Islamic State group to attack targets in France along with Reda Kriket, who was arrested near Paris last week.

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