Police at Brussels airport have claimed at least 50 Islamic State supporters are working there as baggage handlers, cleaners and catering staff.

In an astonishing open letter, the officers said they have warned about the terrorist sympathisers whose security badges give them access to planes, but they remain employed.

The airport police, who are threatening to go on strike because of security deficiencies, also said they have raised the issue of terrorists scouting the airport to plan possible attacks.

Police at Brussels airport have claimed at least 50 Islamic State supporters are working there as baggage handlers, cleaners and catering staff. A soldier is pictured at the airport today

The extraordinary claims come after the Mail reported how the family of two of the bombers involved in the attacks last week said they had worked as cleaners at the airport.

‘Some people suspected of having fought in Syria came to the airport as “false tourists”. We reported their presence but we do not know if anything was done with that information,’ the airport police wrote in their letter.

The officers said they had raised suspicions about certain staff members including those who apparently celebrated after the Paris attacks in November that killed 130 people.

‘When we checked these people, we were surprised more than once. It was men with a radical ideology and a long police history,’ the officers continued.

‘Even today, there are at least 50 supporters of the Islamic state who work at the airport. They have a security badge and have access to the cockpit of a plane.

In an astonishing open letter, the officers said they have warned about the terrorist sympathisers whose security badges give them access to planes, but they remain employed

‘In the past, a number of people had their badges revoked because they had IS sympathies. But clearly not everyone, especially in store personnel, cleaning services and baggage where we find the most suspicious people.’

Police raised concerns about inadequate security at the airport just four days before the attack took place.

The Belgian police union, NSPV, told the interior ministry on Friday 18 March that they would go on strike unless it was improved.

Alain Peeters, the general secretary, said: ‘The sad events of 22 March demonstrate that our concerns are justified. We demand more security and more staff.’

Officers have said that they will not return to work when the airport re-opens unless staffing numbers are increased and that no vehicles can approach within 100 metres of the temporary check-in hall that is being built.

The airport police, who are threatening to go on strike because of security deficiencies, also said they have raised the issue of terrorists scouting the airport to plan possible attacks

The police have complained that they are not sufficiently resourced and do not have enough new uniforms to go around let alone the most up-to-date weapons.

An uncle of Ibrahim and Khalid el-Bakraoui last week told how the brothers had been employed at the airport and would have gained intimate knowledge of the terminal destroyed in the carnage.

The man, who asked not to be named, told the Mail: 'They worked cleaning at the airport and in a restaurant. They didn't finish high school in the end. They cleaned the airport in the summer months.'

Ibrahim, 29, and bomb-maker Najim Laachraoui detonated suitcase bombs in the airport. A third man, only known as ‘the man in the hat’ or ‘the man in white’ was also seen on airport CCTV but ran when his bomb failed to explode.