Ministers must 'resign' over Monis letter

The opposition is demanding resignations over the federal government's "cover up" of the botched handling of a letter from Sydney siege gunman Man Haron Monis.

New documents show Prime Minister Tony Abbott's office knew on June 1 that Julie Bishop had inadvertently relied on incorrect evidence to tell parliament the gunman's letter to the attorney-general's department was sent to a high-level review.

But the foreign minister didn't correct the record until three days later, explaining the letter was not handed over because of an administrative error.

Labor frontbencher Penny Wong accused the government of going to "extraordinary lengths" to cover up the fact it misled parliament.

"The prime minister needs to come clean on the cover-up that his office appears to have been part of," she told reporters in Sydney on Saturday.

"Ministers who deliberately mislead the parliament should resign."