Greste draws strength from public support

Detained Australian journalist Peter Greste has made an emotional plea for release before his next Cairo court appearance which will come, ironically, on World Press Freedom Day.

Mr Greste penned the message inside Mulhaq Al Masra prison, where he's held along with Al Jazeera colleagues Mohamed Fahmy and Baher Mohamed, on the eve of their seventh court hearing on Saturday.

They've been detained for 125 days for allegedly colluding with the Muslim Brotherhood movement and falsely portraying Egypt as being in a state of "civil war" since president Mohamed Morsi's overthrow by the army last July.

Mr Greste said he and local journalists also jailed are deeply moved and strengthened by the outpouring of support.

"Our case has become emblematic of the freedom of the press worldwide," he said.

"What began as a campaign to put down Islamic militancy has been extended to everyone who in the government's words spreads the ideology of terror.

"If by arresting us, the government sought to send a message to journalists both foreign and local working here, then the campaign for our release has sent an unequivocal response."

Mr Greste's letter will be read by his father Juris to hundreds of the journalist's colleagues and supporters at the annual Press Freedom Australia dinner in Sydney.