The RCMP will take over operational command of all security on Parliament Hill in a major shakeup of the way Canada protects its seat of democracy in response to the Oct. 22 attacks in which a gunman stormed Centre Block, sources say.

The aim is to avoid a repeat of the slow response time and communication confusion that characterized the protective response last fall, when multiple security forces were in charge on the Hill.

The federal government will announce the change on Wednesday, a government source said. This means the RCMP will be solely accountable for protecting MPs and senators and their staff, and will be empowered to make decisions about all future security measures on the Hill, including weaponry and infrastructure.

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The RCMP will be responsible not only for the safety of Centre Block, which contains the House of Commons and the Senate Chamber, but all buildings in what is called the Parliamentary Precinct. This includes more than 20 structures between Elgin and Bank streets that face Parliament Hill and run along the north side of Sparks Street. "These are all potential targets," the source said.

The source said an ongoing review of the Oct. 22 attack determined "bureaucratic silos" between security services on the Hill hinder security for MPs, senators and their support staff.

Canada has been targeted for attack by the extremist group the Islamic State. In late January, an IS spokesman threatened new violence against the West, saying adherents in Western countries who have the opportunity to "shed a drop of blood" should do so. "You all saw what one Muslim did in Canada and its infidel Parliament," Abu Mohammed al-Adnani said in a nine-minute recording last month, referring to the October attack in Ottawa.

Before Oct. 22, three security forces oversaw Parliament Hill. The House of Commons Security Services, led by Sergeant-at-Arms Kevin Vickers, was responsible for protecting buildings under the jurisdiction of the House; the Senate Protective Service covered the east portion of Centre Block and East Block, and the RCMP's Parliament Hill detachment was responsible for safety on the grounds.

An RCMP officer yet to be appointed will now oversee an integrated security unit. Ottawa police continue to be responsible for the streets around Parliament Hill.

Changes have already begun.

Mr. Vickers, credited with killing gunman Michael Zehaf-Bibeau on Oct. 22, has been appointed Canada's ambassador to Ireland. A plan to merge the House and Senate security forces was announced last November.

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RCMP officers will not replace House of Commons and Senate security guards on Parliament Hill, the source said. The merger of Senate and Commons guards will continue, and they will still guard Parliamentary offices, but will report to the Mounties.

Government officials worry about what would have happened if the attack on Parliament Hill had involved people with more training and automatic weapons than Mr. Bibeau, who carried only a lever-action rifle.

"This is one of the most important symbols of our democracy, and security on the Hill has to be able to meet the threat environment today," the source said.

The move echoes a 2012 recommendation by Auditor-General Michael Ferguson for a unified security force to protect the Parliamentary Precinct.

The transition to this new security plan for Parliament will be led by the Speakers of the Commons and the Senate, and it will not infringe on elected officials' right to come and go from buildings.