Oil giant Shell's Nigerian subsidiary has declared a force majeure on Bonny Light crude exports following a leak on a key pipeline, AFP news agency reports. 

The declaration of a force majeure excuses a company from contractual agreements when an extraordinary event which is beyond its control occurs.  

Shell's subsidiary did not disclose the volume of production lost from Bonny, which is one of Nigeria's main export terminals.

Bloomberg news agency reports that the pipeline operator, Aieto Exploration and Production Company, has not yet established the cause of the leak. 

"We don't know if it's an attack or sabotage," its spokesman Sola Omole is quoted as saying.