Prime Minister Tony Abbott may have known about a missing letter from Sydney siege perpetrator Man Haron Monis, and may have misled parliament.

A document reported in Fairfax Media suggests Mr Abbott was prepared to answer questions on the missing letter three days before parliament was told it was missing.

The letter was written by Monis and delivered to Attorney-General George Brandis’ office asking whether it was legal to write to the head of Islamic State.

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The letter was withheld from an inquiry on the Sydney siege, a move which a government staffer later apologised for as accidental.

But crucial to the story is the timing of when the oversight was known, and when it was disclosed to the parliament.

The Opposition has said that Foreign Minister Julie Bishop misled parliament over the timing of her disclosure.

Ms Bishop told the parliament on June 4 the missing letter wasn’t shown to the inquiry, but the Prime Minister may have known about the issue on June 1, Fairfax reported.

A PPQ document, which is a pre-prepared answer to questions the government expects to be asked during Question Time, was made for Mr Abbott on June 1. The document was emailed to another official three hours before Question Time on the day, giving the Prime Minister time to acknowledge the missing letter and correct the record.

It’s not clear whether he saw the PPQ, but the document was drafted by his department’s second in charge.

The Opposition’s Penny Wong has switched her attack from Ms Bishop to Mr Abbott.

“The Prime Minister cannot continue to duck questions about the part he and his office played in this cover-up. The Prime Minister is accountable for this cover-up,” she said.