Vienna (AFP) - Austrian police have arrested several security employees at Vienna airport over their alleged role in smuggling illegal immigrants to Britain and the US, officials confirmed on Tuesday.

Six people were detained, although four of them have been released, public prosecutor Friedrich Koehl told AFP.

"In total, 13 people are being investigated in connection with the case, which was launched at the end of February," he said.

The suspects, mainly Austrian and Sri Lankan nationals, worked for private security firms hired by Austrian Airlines (AUA) to carry out passport and ticket controls at the boarding gate.

Thanks to their own security clearances, the men were able to smuggle refugees from Sri Lanka past checkpoints and provide them with boarding passes, said Koehl.

In exchange, they allegedly received between 7,000 ($7,630) and 9,000 euros per migrant.

Security firm G4S confirmed one of its employees had been involved in the smuggling ring.

The suspect was "immediately fired", the firm said, adding that it would tighten its airport control procedures and carry out more thorough background checks during the hiring process of new staff.

Meanwhile, AUA said it would address the issue internally with the security firms.