Prime Minister Justin Trudeau has denied interfering in an investigation into Canada's worst mass shooting.

The head of the RCMP, Canada's federal police force, has been accused of pressuring local officers to help advance Mr Trudeau's gun control plans.

Commissioner Brenda Lucki has denied any meddling in the investigation.

The accusation stems from notes made by a local RCMP officer, released as part of a public investigation into the mass shooting.

Speaking at a press conference on Thursday, Mr Trudeau said his government "did not put any undue influence or pressure" on police.

"It is extremely important to highlight that it is only the RCMP, it is only police that determine what and when to release information."

On 18-19 April 2020, a gunman posing as a police officer killed 22 people in the province of Nova Scotia. The suspect died in a stand-off with police.

The Halifax Examiner was first to report the account of Nova Scotia RCMP Superintendent Darren Campbell, whose notes were written after a conference call with Ms Lucki - Canada's top police officer.

The call took place on 28 April 2020, just over a week after the shooting and days before Mr Trudeau's Liberal government announced a ban on semi-automatic weapons.

"The Commissioner said she had promised the minister of public safety and the Prime Minister's Office that the RCMP would release this information," he wrote, about Ms Lucki's reaction to press briefings carried out by the RCMP in Nova Scotia.

"The Commissioner then said that we didn't understand that this was tied to pending gun control legislation that would make officers and the public safer."

Mr Campbell recalled in the notes how the commissioner had been angry that his press conference did not disclose more details about the types of weapons used during the rampage.

The Nova Scotia RCMP communications team had decided not to release information about the firearms out of concern it would jeopardise the investigation - being carried out by Canadian and US law enforcement - into the suspect's access to the guns, according to notes from the inquiry.

Mr Campbell said the commissioner's dressing down had reduced officers "to tears".

According to former RCMP communications director Lia Scanlan, Ms Lucki was asked not to give media interviews in the immediate aftermath of the shooting but did so anyway, giving inaccurate information in the process.

"The commissioner releases a body count that we (RCMP communications) don't even have," Ms Scanlan told a lawyer for the public inquiry. "She [Ms Lucki] went out and did that. It was all political pressure. That is 100% Minister Blair and the Prime Minister. And we have a Commissioner that does not push back."

In a statement released on Tuesday, Ms Lucki said information sharing between the federal government and police is normal during a high-profile event such as a mass shooting, but acknowledged she "should have been more sensitive" in her approach.

Mr Trudeau's minister of public safety at the time of the shooting, Bill Blair, has also denied wrongdoing and questioned Mr Campbell's account.

"The superintendent obviously came to his own conclusions and his notes reflect that," Mr Blair told media.

The Conservative Party has called for a debate in the House of Commons, and a parliamentary committee voted on Thursday to hold a hearing into the matter.

Lawyers for the shooting victims' families said they will ask Mr Blair and former Nova Scotia justice minister Mark Furey to appear before the ongoing joint federal and provincial inquiry into the April 2020 mass shooting, to testify on whether there was political interference.