A North Korean radio, monitored here, broadcast coded numbers Friday, in what could be a secret message to North Korean spies operating in South Korea.

In the broadcast at 01:15 a.m., a state-run Radio Pyongyang announcer said, "I'll let the members of the No. 27 expedition know of review tasks in chemistry of the distance education university from now on."

"No. 51 on Page 428, No. 33 on Page 192, No. 41 on Page 260...," the announcer read.

The numbers were repeated once again, which are new compared to ones in previous broadcasts.

The North has broadcast coded numbers 22 times since June 24, with the latest one made on Sunday.

In the past, Pyongyang would send such broadcasts at midnight to issue orders to its secret agents hiding in the South.

The communist country suspended the cipher broadcast after inter-Korean summit talks in 2000 and resumed it last year. (Yonhap)