SEOUL (Reuters) - North Korea on Wednesday threatened a military strike against the South a day after Seoul joined a U.S.-led initiative to intercept shipments suspected of being involved in weapons of mass destruction.

"Any hostile act against our peaceful vessels including search and seizure will be considered an unpardonable infringement on our sovereignty and we will immediately respond with a powerful military strike," a spokesman for the North's army was quoted as saying by official KCNA news agency.

(Reporting by Jack Kim; Editing by Jon Herskovitz)