North Korea's state radio has recently broadcast strings of indecipherable numbers in a possible resumption of a Cold War-era method of sending coded messages to spies operating in South Korea.

Seoul's Unification Ministry said Tuesday that a female announcer at the radio station read numbers for 2 minutes on June 24 and 14 minutes on Friday. It says the broadcast included phrases such as "No. 35 on Page 459" and "No. 55 on Page 913."

During the Cold War, Pyongyang sent such numbers via shortwave radio to give missions to agents dispatched to South Korea. It later reportedly stopped such broadcasts once it could communicate with its spies overseas via the internet.

Some experts view the latest broadcasts as a North Korean attempt to wage psychological warfare against Seoul.