A female announcer at Radio Pyongyang read numbers for minutes at 1:15 a.m. (local time), calling out numbers, such as "No. 18 on Page 451."

The announcer said she is "giving review work in foreign language lessons of the remote education university for No. 27 expedition agents."

Broadcasts of mysterious numbers were used by North Korea to give missions to spies operating in South Korea in the past. Spies could decode the numbers to get orders by using a reference book.

Since June, North Korea has broadcast such numbers on 36 occasions including 16 this year.

Experts are divided over whether North Korea is sending instructions for espionage missions in its latest broadcasts. Some analysts said the move is a deceptive strategy aimed at sparking tension within South Korea.

"It is hard to definitely say what pattern North Korea's number broadcasts has or what its intent is," said Lee Eugene, vice spokesperson at Seoul's unification ministry. (Yonhap)