A crude oil leak in central Alberta's Strathcona County on the afternoon of April 21 came from Inter Pipeline Ltd.'s Cold Lake regional pipeline system, the company said in a statement on April 24.

Calgary, Alberta-based Inter Pipeline has isolated a segment of the pipeline near its Strathcona Terminal in Edmonton for repairs and said it is working with regulators to investigate the cause of the incident.

There were no details on how much crude was released but the company said the spill was contained on April 21 and clean-up efforts were ongoing.

"Inter Pipeline will assume the role of lead responder for this incident today and will continue to ensure public safety and protection of the environment are the top priorities," the company said.

A number of energy companies have pipelines in the area and when the leak was first reported around 12:30 p.m. on April 21 its origin was not immediately clear.

Four companies including Inter Pipeline shut in and de-pressurized pipelines, CBC News reported.

Of those, Imperial Oil Ltd. (NYSE MKT: IMO) has received approval from the regulator to restart its lines and Gibson Energy Inc. said it resumed shipping crude in the afternoon of April 23. Pembina Pipeline Corp. (NYSE: PBA) did not immediately respond to a request for comment.

The 558,000 barrel-per-day Cold Lake pipeline system transports diluted oil sands bitumen from the Cold Lake region in northern Alberta to the Edmonton marketing hub for shippers including Imperial, Canadian Natural Resources Ltd. (NYSE: CNQ) and Cenovus Energy Inc. (NYSE: CVE), according to Inter Pipeline's website.

Imperial said there was no impact to operations outside the Strathcona County region when asked if the pipeline outage had affected oil sands production. Canadian Natural and Cenovus did not immediately respond to requests for comment.