ASIO sought to access journalists' data

Australia's security and intelligence agency has revealed it sought to access a "small" number of journalists' telecommunications data.

But ASIO Director-General Duncan Lewis said he could not publicly divulge how many journalist information warrants had been obtained.

"The numbers are small and a simple exercise in deduction would start to throw light on the investigations that are currently underway," he told a Senate estimates hearing on Tuesday night.

The warrants, issued to ASIO by Attorney-General George Brandis, were part of the federal government's sweeping data retention laws introduced in 2015.

Crossbench senator Nick Xenophon, who was pushing for the details, said the reasons for withholding the information "just don't cut it".

"The level of secrecy surrounding Journalist Information Warrants is ridiculous," he tweeted.