WINNIPEG -- RCMP officers are looking for the caller who made serious threats, including a bomb threat, against a Portage la Prairie, Man., high school, sending it into a lockdown.

As CTV News Winnipeg previously reported, the Portage Collegiate Institute was placed into a hold and secure on Wednesday morning. RCMP said officers in Portage la Prairie received a call around 11 a.m. from an unknown person who made multiple "serious threats" against the school, which included a threat about an explosive device.

RCMP contacted an officer at the school, who was there for an unrelated matter, and asked that the school be placed on lockdown.

Multiple officers from the Portage la Prairie detachment responded to the threat, as well as the Police Dog Services who brought a certified explosives detection dog.

"A thorough search of the area was completed by officers and Police Dog Services with no suspicious persons or items being located," RCMP said in a news release.

Following the search, the lockdown was lifted. In a letter sent home to parents, the school's principal said the school reopened shortly before 2 p.m.

RCMP detained two people for questioning, but both people were released after it was determined they were not involved.

"The RCMP is continuing its investigation and is now focussing on identifying the caller," RCMP said.

Anyone with information is asked to call Portage la Prairie RCMP at 204-857-4445, or call Crime Stoppers anonymously at 1-800-222-8477, or the secure tip online.