Smoke bombs disrupt service on Montreal subways
Smoke bombs were set off in several subway stations in Montreal, Canada, temporarily halting service during rush hour, police say.
Most subways were operating normally by 10:00 (14:00 GMT), and there were no reports of injuries.
Thousands of commuters were stranded on Thursday morning, with traffic jams and long queues at bus stops as a result.
Montreal's subway service has been disrupted in recent weeks by student protests over rising tuition fees.
However, police have not linked Thursday's incident with the student protests.
Police say they found three smoke bombs after receiving dozens of phone calls about heavy smoke in some stations. They have not attributed blame for the attacks.
"There are five teams of investigators... on the field right now to try to establish exactly who did this," Simon Delorme, media officer for Montreal police, told the Reuters news agency.
Quebec Premier Jean Charest has denounced the incident, adding that he hopes the perpetrators are found.