An Australian national who recently returned to the country after living overseas has been arrested for allegedly selling sensitive information to a foreign intelligence service, police said.

The Australian Federal Police said Alexander Csergo, 55, had been compiling reports for two foreign spies known to him as “Ken” and “Evelyn”.

The pair offered to pay Csergo for information on Australia’s “national security arrangements”, police said, without naming which intelligence agency they were allegedly working for.

“Espionage and foreign interference pose a serious threat to Australia’s sovereignty, security and integrity of our national institutions,” police added.

Csergo, an IT and marketing specialist, was arrested in Sydney on Friday evening, and briefly appeared in a local court via video link on Saturday morning.

He was first approached while he was working overseas by an individual who claimed to be representing a think-tank, police sad.

That individual arranged for Csergo to meet the pair known as “Ken” and “Evelyn”.

Assistant police commissioner Krissy Barrett said Ken and Evelyn work for a “foreign intelligence service and are undertaking intelligence collection activities”.

Barrett said other Australians may have been approached.

Csergo is charged with one count of “reckless foreign interference” – carrying a maximum prison sentence of 15 years – and is just the second person to be charged under anti-spying laws passed by the former conservative government in 2018.

He is due to reappear in court on Monday.