The ABC board has revealed that it did take immediate action on allegations made by former managing director Michelle Guthrie, including a claim that former chairman Justin Milne called for journalists to be sacked.

After growing calls for the board to explain what action it took to protect the ABC’s independence, the board finally released a statement on Thursday saying it undertook to hold an investigation into Guthrie’s claims the night before she was sacked.

The board, led by the interim chair Kirstin Ferguson after Milne resigned in the wake of the interference revelations, said it has always ensured editorial independence is maintained.

Guthrie’s letter alleged Milne called for economics correspondent Emma Alberici to be sacked and political editor Andrew Probyn to be “shot” as well as other claims that he was acting to appease the Coalition government. “They [the government] hate her,” Milne wrote in a leaked email in reference to Alberici. “Get rid of her.” The board decided to appoint an external investigator but proceeded to sack Guthrie the following day.

Because ABC Guthrie vs Milne scandal involves grave allegations of political (“get rid of her” “shoot him”) interference, Federal Parliament must urgently establish a public inquiry. All documents must be tabled; Milne, Guthrie, all directors/executives called. https://t.co/N8u9V2ozuX — Quentin Dempster (@QuentinDempster) October 4, 2018

“To clarify various media reports, the board received a letter from the former managing director late on Friday 21 September 2018,” the board said.

“In that letter, Ms Guthrie responded to several issues that the board raised with her. In addition, the former managing director raised other matters that she requested the board investigate on a confidential basis.

“The board resolved on Sunday 23 September 2018 to appoint an external, independent expert advisor to investigate these matters. That investigation is under way, and it is not appropriate for the board or the ABC to make any further comment pending its completion.

“[The ] board has always acted in the best interests of the ABC, has fully debated any issues presented to it and ensured that editorial independence has been maintained. We are united in defending the independence of the corporation. We have done our job thoughtfully and with due regard to board process.

“The board is focused on supporting the acting managing director David Anderson, his leadership team and all employees in fulfilling the ABC’s charter remit and serving the community.”

The statement came a week after Milne resigned amid claims of political interference. Ferguson had refused to address the claims in an interview last week and this fuelled questions about the board’s actions.

Last week Ferguson said the board had always acted independently but declined to reveal what action she had taken in the face of Milne’s alleged interference.

“I understand there is genuine public concern about the events of the past week and I want to make it clear we share these concerns,” Ferguson said. “We believe in the values of the ABC and we will cooperate with the departmental inquiry announced by Minister Fifield in accordance with the ABC Act.”

Communications minister Mitch Fifield has ordered the department of communications to undertake an inquiry and has started the process of appointing a new chair.