LONDON — The suicide attacks at Brussels Airport have led to intensified scrutiny of hiring, security and the lack of standardized procedures at airports across Europe, amid questions about whether the bombings last week could have been prevented.
The head of the largest police union in Belgium warned on Thursday of a serious security problem at Brussels Airport, citing systematic security flaws, bureaucratic incompetence and the employment of baggage handlers with criminal records.
His remarks came as the airport police wrote an open letter, cited in several Belgian newspapers, expressing deep concern about the level of security at the airport, echoing worries about procedures, staffing and the potential for infiltration by terrorists at Paris Charles de Gaulle Airport after the deadly attacks in and near Paris in November.
Since 2001, the European Union has adopted a uniform set of rules and procedures for protecting the areas of any airport that are behind security checkpoints. But the methods for safeguarding of areas accessible to the general public are established at a national level and therefore vary among member states.
Vincent Gilles, president of SLFP Police, the largest police union in Belgium, with 22,000 members, said in a telephone interview that he was disturbed after hearing colleagues say that some baggage handlers had applauded the attacks in Paris that killed 130 people.
“This is what I have heard from fellow police,” he said. “Obviously, one needs to be prudent and we are checking this out.”
Mr. Gilles said there was a notable and worrying number of employees working at Brussels Airport in baggage handling and on the tarmac who had criminal records, but he did not provide an estimate.
Many of the terrorists involved in the Brussels and Paris attacks have links to the poorer, immigrant parts in the Belgian capital, and Mr. Gilles appeared to draw a connection between those areas and the security of the airport. Mr. Gilles suggested that the recruitment policy employed by the Brussels Airport Company, which manages the facility, appeared to favor people from those areas.
Anke Fransen, a Brussels Airport spokeswoman, said the company was aware of the various concerns raised by the police union but had no immediate comment.
The Brussels Airport Company said in a statement Thursday that it was “operationally ready” to reopen and that the Belgian Civil Aviation Authority had granted approval for a partial restart of passenger flights. The authorities had not made a formal decision on when they could resume, however, and there will be no flights before Friday evening, the statement said.
Concerns about security and the potential risk of infiltration by radical groups has been a concern at airports around Europe. In the days after the attacks in France, the police raided about 4,000 employee lockers at Charles de Gaulle, Europe’s second-largest airport, in search of evidence potentially linking staff to the attackers or other Islamist groups.
According to police and union officials, those searches yielded little more than a small cache of Qurans and other Islamic literature. (The searches led to the dismissal of about a dozen employees, who were found in possession of food or other goods stolen from airport vendors.)
Nonetheless, the airport’s chief of police, Philippe Riffaut, has used the threat of terrorism to justify a review of the roughly 87,000 airport employees who have badges giving them access to secure areas that include the tarmac, baggage handling and cargo storage.
Those badges, issued after a background check by the police, are normally renewed every three to five years. Since January 2015, the police said, the badges of more than 80 workers at Charles de Gaulle have been revoked for security reasons.
In Brussels, Mr. Gilles said that while traffic at the airport had increased tenfold over the past 15 years, his repeated requests to augment security had been ignored. He said that was because the federal police, who are responsible for the airport, saw it as unnecessary and failed to send the request up the chain of command to the Interior ministry.
Mr. Gilles suggested that bureaucratic entropy and a lack of responsibility among the political class were undermining security at the airport.
Belgium, a politically fragmented and linguistically divided country, has come under heavy criticism in recent days after a number of astonishing law enforcement and intelligence errors leading up to the deadly attacks at the airport and the Maelbeek subway station in Brussels.
Mr. Gilles accused the Brussels Airport Company of placing an excessive focus on economic considerations, and he said a request made in December to install a security check outside the entrance to airport terminal had been rebuffed.
He said he was told that such a checkpoint would be too expensive, and that company officials defended the decision by noting that no other airport in the European Union’s open-border Schengen Area had such security measures.
In the open letter by the airport police, as reported on Thursday by Het Belang van Limburg, a Flemish newspaper, the officers said they were not satisfied with security.
They complained that employees of all ranks had access throughout the airport, and that there were insufficient checks on passengers before they entered the terminal to check in for flights.
Mr. Gilles told RTL, the Belgian broadcaster, that the letter was not a negotiating tactic but a cry for help, and that security workers had been complaining about conditions for more than a year.
In the interview with RTL, he said that fatigue among airport staff members extended to those involved in counterterrorism. He said the police were enraged about the targeting of Brussels. “There is anger for not having prevented the attacks,” he said.