The Quebec police force admits that three masked protesters at the Montebello summit were undercover officers -- the same men accused of trying to incite violence.

Quebec police released a statement Thursday night saying its officers posed as protesters but did not act illegally.

"At no time did the Quebec provincial police officers act as agents provocateurs or commit criminal acts," the force said.

"Also, it is not part of the policy of the police force nor is it part of its strategy to act in this manner. At all times, the officers responded to their mandate to maintain law and order."

Dave Coles, president of the Communications, Energy and Paperworkers Union of Canada, has alleged the three masked men had acted as agents provocateurs.

A video posted on YouTube from Monday's protests in Montebello, Que. shows Coles in a confrontation with the men.

He tells them to remove their masks. One of the three men is holding a rock and Coles tells him to move because their line is meant for peaceful protesters.

"These three guys are cops, everybody!" Coles can be heard shouting to the crowd as he tries to pull down their bandanas.

The three men then push their way into the police line and appear to be arrested, then taken away.

Police said that after viewing the clip, they were able to confirm the men were Quebec provincial police officers.

Photographs taken by another protester had shown the three men lying on the ground with the soles of their boots adorned by yellow octagons. A police officer kneeling beside the men appeared to have the same imprint on his boot -- likely the Vibram boots logo.

The Liberals have called for a police probe in the matter, and the NDP have asked Public Safety Minister Stockwell Day to launch a public inquiry.

"If they are police officers, and if they are stepping forward with a mandate to disrupt in any way, that's a cause for concern," New Democrat MP Peter Julian told The Canadian Press.

But Day has said there will be no investigation into the incident.

"I've made the inquiries and there was no RCMP that were involved as far as those three individuals go," he told reporters in Winnipeg.

"If people have concerns ... there is a complaints process for the RCMP. There is also one for the Surete du Quebec. This incident happened in Quebec, so I imagine people could also file under that complaints process."

Both the RCMP and Quebec police had denied using undercover officers to antagonize peaceful demonstrators.

"I confirm (to) you that there is no agents provocateurs in the Surete du Quebec... It doesn't exist in the Surete du Quebec," spokesperson Const. Melanie Larouche told The Canadian Press Wednesday.

RCMP Cpl. Luc Bessette said the Mounties do "not use tactics that would encourage confrontation or incite violence."

With files from The Canadian Press