RCMP investigators executed a search warrant Friday at the Montreal headquarters of engineering giant SNC-Lavalin, which has been probing millions of dollars of mysterious payments.

Two officers stood guard in the building's lobby at midday and prevented journalists from entering the building.

SNC-Lavalin said it had no warning of the RCMP search but will co-operate with the investigation.

"It's important to understand that we have been forthcoming and as transparent as we can be, and have actually initiated certain conversations in order to show complete co-operation and collaboration," SNC-Lavalin spokeswoman Leslie Quinton said.

Reporters wait for a comment from the RCMP outside SNC's headquarters. (Morgan Dunlop/CBC)

In an earlier statement, the company explained the warrant is linked to an investigation of "certain individuals who are not or are no longer employed by the company."

The company said it would provide no further comment.

SNC-Lavalin asked the RCMP earlier this year to investigate after two top executives resigned amid allegations of wrongdoing.

The request came after an internal audit into payments worth $56 million US that resulted in the resignation of company CEO Pierre Duhaime and two other senior executives — vice-president Stéphane Roy and executive VP of construction Riadh Ben Aissa.

SNC has been under pressure to explain the mysterious payments.

'The warrant relates to an investigation of certain individuals who are not or are no longer employed by the company.'

—Statement from SNC-Lavalin

Duhaime stepped aside after the internal probe reported he signed off on the payments, made to undisclosed agents on two large projects. The authorization breached SNC's code of ethics.

SNC-Lavalin has refused to indicate the whereabouts of the projects involved, or rule out whether they included construction projects in Canada. However, the company has said that it didn't believe the payments in question were related to its operations in Libya.

SNC was one of the major Canadian companies doing business in the North African country prior to the fall of the late Libyan dictator Moammar Gadhafi last year.

SNC-Lavalin's recent troubles began when its name surfaced in connection with a Canadian consultant, Cyndy Vanier, who was arrested in Mexico on suspicion she had tried to smuggle members of Gadhafi's family into Mexico.

RCMP questioned Vanier in prison

Vanier has told CBC News that two officers from the RCMP's commercial crimes section visited her in her Mexican prison in mid-March.

She said they told her she was a witness, not a suspect, as they asked dozens of questions about her business dealings with SNC-Lavalin, specifically the two executives who hired her, Roy and Ben Aissa.

Vanier said she answered questions and signed statements for the RCMP until 4 a.m. on March 22.

The RCMP searches weren't unexpected given that in the company's last quarterly conference, management indicated they were handing over the results of their own internal investigation to authorities, said Neil Linsdell, an analyst who covers SNC for research firm Versant Partners.

"This seems like a logical follow-up... for the RCMP to make," he said.

On the TSX, SNC shares were down Friday by seven per cent, to $37.67.

Pierre Duhaime will remain an SNC employee until June 27 but will not have any responsibilities or take any policy-making decisions, the company said in a regulatory filing ahead of its May annual meeting.

Duhaime is slated to receive nearly $5 million as a severance package after he was relieved of his duties.

With files from Canadian Press