OTTAWA (AFP) - Canadian police have released dramatic surveillance footage showing the moment a gunman suspected of planning to travel to Syria to fight alongside Islamic militants breached security at parliament after shooting dead a soldier.

The footage emerged on Thursday as officials said they had found no evidence of a wider plot following another deadly attack on Monday - also by a young Canadian convert to Islam who had sought to leave for Syria.

Watch the Parliament Hill security video footage of the gunman here.

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.

Canadian authorities were scrambling to probe the background of the young men, the first of whom ran his car over a soldier, killing him, and another who shot the soldier at a war memorial before storming parliament and being gunned down.

"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."

Paulson said the gunman in Wednesday's attack on parliament, identified as 32-year-old Michael Zehaf-Bibeau, had been in Ottawa applying for a passport to travel to war-torn Syria.

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

His comments came as video surveillance footage showed how the young gunman took less than four minutes to gun down army reservist Corporal Nathan Cirillo and make his way into parliament, where he exchanged fire with police and parliamentary security.

Canada has never before been hit by Islamist violence, but it has been threatened in militant broadcasts over its role in US-led air strikes on the Islamic State group in Iraq.

Some Canadians are thought to have traveled to the Middle East to join the group, and others are thought to have developed radical ideas at home, living among Canada's Muslim minority.