Montreal police are investigating after someone set off a suspected smoke bomb on the green line of the metro Wednesday morning.

The incident happened just before 7:20 a.m., when police received a 911 call about smoke in the metro tunnel between the Beaudry and Papineau stations.

"Officers did a security check and they found a suspicious object between the stations," said Const. Daniel Fortier.

Several reports from the scene Wednesday morning described the object as a smoke bomb.

Police wouldn't confirm that, but said an investigation is underway to determine if the object recovered was related to the smoke.

Montreal’s transit authority said service was temporarily halted between the Lionel-Groulx and Honoré-Beaugrand stations.

Service was restored by 8:15 a.m.

Other deliberate metro shut downs caused commuter angst earlier this week.

A coordinated attack saw emergency brakes pulled at five stations and bags filled with bricks thrown on the tracks on Monday morning.

Also on Monday, a smoke bomb was set off in the Berri-UQAM metro station.

Police are still investigating those incidents.

Fortier said there's been no stepping up of security in the metro system despite the incidents of mischief.

"The security measures are plenty good always, so the investigators are [focusing] on using the cameras in the metro and we're going to investigate the case," he said.