- Radio broadcast may have been a book cipher for spies in other countries
- Message for 'agents' included numbers, which spies can decode with book
- It is the third message of its kind this month and the 14th since late June
- South Korea believe an attack could take place after movement of missiles
By Anthony Joseph for MailOnline
Published: 04:42 EST, 21 November 2016 | Updated: 15:38 EST, 21 November 2016
North Korea has broadcast a 'coded message' to sleeper agents on state radio - sparking fears of an imminent attack.
The announcement was made as part of a cryptic broadcast and analysts believe it is a 'book cipher' for agents in foreign countries.
The radio announcer said: '(I'm giving) chemistry review work to No 21 expedition agents,' before continuing with the numbers, which spies can decode using a reference book.
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