Canada's capital faced a third day of heightened security on Friday as police searched for any clues that the attacker who shot and killed a soldier and charged into the parliament building had help in plotting his attack.

The Royal Canadian Mounted Police ordered a detail of officers to remain with Prime Minister Stephen Harper, 24 hours a day, seven days a week, after it emerged that he briefly hid in a closet-like room during Wednesday's attack.

Michael Zehaf-Bibeau, a 32-year-old Canadian citizen with a record of criminal drug violations was named by police as having carried out the brazen attack. He had undergone a "radicalization process" and applied recently for a passport, hoping to travel to Syria, police said.

He had no apparent links to Martin Rouleau, a 25-year-old convert to Islam who two days earlier drove over two Canadian soldiers, killing one, in Quebec, police said.

Both men were shot dead by security officers.

The attacks took place in a week when Canada sent six warplanes to the Middle East to participate in US-led air strikes against IS militants.

The prospect of more such strikes was at the forefront of many minds in Canada, as a society proud of its reputation for openness and tolerance grappled with a new menace.

"These are difficult threats to detect," Royal Canadian Mounted Police Commissioner Bob Paulson said. "There is no way of knowing where or when such an attack could take place."

It remained unclear whether Zehaf-Bibeau "received any support in the planning of his attack," he added.