SYDNEY (AFP) - A radio station at the centre of a prank call targeting Prince William's pregnant wife Catherine that led to the suicide of a nurse is trying to block further investigation of its actions, Australia's communications watchdog said on Thursday.

The Sydney broadcaster, 2Day FM, has applied to the Federal Court for an order restraining the Australian Communications and Media Authority (ACMA) from continuing its probe into the December 2012 call.

British nurse and mother-of-two Jacintha Saldanha took the hoax call from two DJs pretending to be Queen Elizabeth II and Prince William's father Prince Charles, before passing it onto a colleague who divulged details of Kate's morning sickness.

The broadcast of the prank made global headlines and Saldanha was found hanged three days later, triggering a major backlash against the radio network and the hosts.

The ACMA began investigating 2Day FM, including an examination of whether the prank call breached its broadcasting licence and the commercial radio codes of practice.

But the radio station is now trying to stop it going any further.

"On 18 June 2013, in response to the ACMA's preliminary findings on this issue, Today FM applied to the Federal Court for orders restraining the ACMA from continuing the investigation and making a finding that Today FM breached that condition," the watchdog said in a statement.

"The ACMA intends to contest Today FM's application." The radio station, which earlier this month controversially named one of the DJs involved, Michael Christian, as its "Top Jock", could not immediately be reached for comment.

Kate and William's baby, which will be third in line to the throne, is expected in mid-July.

The heavily pregnant duchess on Saturday made her last public appearance before giving birth, attending the Trooping the Colour military parade in London celebrating the queen's 87th birthday.