King Charles sends Kim Jong-Un message as he heads to Russia to meet Putin

It comes on the same day that the North Korean leader is expected to visit Russia's far-eastern port city of Vladivostok by armoured train this month to meet President Vladimir Putin, possibly to discuss supplying Russia with weapons for its war with Ukraine.

The trip, which has not been officially confirmed, would be his first visit abroad in more than four years and the first since the coronavirus pandemic.

It is likely to take almost a full day to travel more than 1,000 km (600 miles) to Vladivostok across the border with Russia, taking account of the North's sometimes archaic rail network.

While he has made more trips abroad than his father, Kim Jong Il, as leader, Kim's travel is often shrouded in secrecy and heavy security. Unlike his father who was said to be averse to flying, Kim has flown his personal Russian-made jet for some of his trips.

In 2004, there was a huge explosion at a rail station near the Chinese border after Kim Jong Il passed on train returning from China, killing more than 100 people. The cause, and whether it was an assassination attempt, were never confirmed.

The train, with its signature green paint, is believed to include more than 20 armoured cars and equipped with a communications system and a special cabin for Kim with a bright white interior where he has been seen at work and holding meetings with aides, according to North Korea's official media and South Korean analysts.