Australian embassies are part of a US-led global spying network and are being secretly used to intercept calls and data across Asia, local media reported on Thursday.

The top secret Defense Signals Directorate operates the clandestine surveillance facilities at embassies without the knowledge of most Australian diplomats, Australia's Fairfax Media reports.

"Fairfax Media has been told that signals intelligence collection takes place from embassies in Jakarta, Bangkok, Hanoi, Beijing and Dili, and High Commissions in Kuala Lumpur and Port Moresby, as well as other diplomatic posts," Fairfax said on Thursday.

Some of the details are revealed in a secret US National Security Agency document leaked by exiled American former CIA employer and whistle-blower Edward Snowden and published by Germany's Der Spiegel.

The document shows the existence of a highly sensitive signals intelligence collection program, codenamed STATEROOM, conducted from sites at US embassies and consulates and from the diplomatic missions of other intelligence partners including Australia, Britain and Canada.

"They (the surveillance facilities) are covert, and their true mission is not known by the majority of the diplomatic staff at the facility where they are assigned," the document says.

A former Australian Defense Intelligence officer has told Fairfax Media the directorate conducts surveillance operations from Australian embassies across Asia and the Pacific.

The Department of Foreign Affairs and Trade declined to comment on "intelligence matters," Fairfax said.

"It is the long-standing practice of Australian governments not to comment on intelligence matters," a departmental spokesperson told Fairfax.