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.

The North Korean government released pictures of Kim Jong Un attending a firing contest among women gunners of the multiple launch rocket system at the weekend

North Korea has broadcast a 'coded message' to sleeper agents on state radio - sparking fears of an imminent attack

Similar broadcasts were reportedly made on November 6 and 11 and the latest is the 14th since June.

A source in the South Korean ministry told the Daily Star that their neighbours could launch an attack 'at any time'.

They have also detected many missiles moving around the country.

Meanwhile, at the weekend it emerged that North Korean dictator Kim Jong-un has a team of 130 top scientists battling to keep him alive.

Defector Hyeong-soo Kim, Mr Kim, who fled North Korea in 2009, has said a mysterious Longevity Institute works to the sole purpose of preserving the leader's health.

The portly leader reportedly weighs almost 300 pounds and is said to be in poor health

Mr Kim worked at the institute when Kim Jong-un's father Kim Jong-il ruled the country.

Kim Jong-un is renowned for his indulgent diet, and due to his love of fine food and wine, French cheeses, and huge meals, he has piled on the pounds since he came to power.

This means the scientists are facing a constant fight to keep the leader's cardiovascular disease and diabetes at bay.

The situation meant researchers were desperate to study other obese people, but with so many North Koreans starving, they were forced to build their knowledge by spying on overweight foreigners instead - including political leaders.