PETERSON AIR FORCE BASE, Colo. - Canada's defence minister is taking part in a solemn remembrance ceremony today in the U.S.

On the anniversary of the 2001 terrorist attacks, Defence Minister Rob Nicholson has delivered a speech during a ceremony at Colorado's Norad facility, where Canadian and American military personnel work together on continental security.

Nicholson says that as we remember the men and women who died 13 years ago, we must also pledge to keep working to defend the continent so that such a terrible day never occurs again.

The lingering fears over terrorism loom over today's ceremony.

The U.S. deputy secretary of defence was supposed to attend -- but didn't. Robert Work was busy in Washington, dealing with the fallout from President Barack Obama's speech announcing plans to expand the fight against Islamist rebels in Iraq, and now Syria.

Speaking at the ceremony, Norad commander Charles Jacoby called the ISIL operation a fitting backdrop to reflect on 9-11.