Transit police have been performing extra security sweeps across the Metro Vancouver SkyTrain system in the wake of Friday’s subway bombing in London.

Officers wearing high-visibility vests and assisted by explosives-detecting dogs did additional checks throughout the morning as a precaution, a spokesperson told CTV News.

There has been no intelligence suggesting any kind of local threat, but police are still encouraging transit users to contact them if they see anything unusual.

Andre Gerolymatos, a terrorism expert at Simon Fraser University, said it's very difficult to prevent terror attacks by ramping up security on the ground. He believes the most effective method is for the intelligence community to root out plots before they happen.

"The solution is good, old-fashioned detective work: find out where these [terrorist] cells are and break them up," Gerolymatos said.

Additional surveillance cameras don't do much to prevent attacks, according to Gerolymatos, and the amount of security it would take to catch someone in the act "would paralyze the transit system."

In 2012, an explosive device was discovered on the SkyTrain tracks in Surrey, prompting a long and intensive investigation. No one was ever arrested, and transit police characterize the incident as a one-off.

Vancouver isn't the only city to heighten security as a result of the London bombing. Precautions are being taken elsewhere, including New York.

Friday's attack, which injured 29 people, is the fourth terror incident committed in London so far this year. It prompted officials to raise Britain's terror level to “critical,” the highest possible, suggesting another attack could be coming.

With files from CTV Vancouver's Penny Daflos