Chinese walls

It is sometimes called the world's last Stalinist dictatorship. North Korea is the most secretive state on the planet. Its prison camps are believed to hold between 80,000 and 120,000 people. The death toll from a famine in the 1990s was somewhere between 600,000 and 3.5m.

Since his father and predecessor Kim Jong-il died in 2011, the new supreme leader Kim Jong-un is thought to have conducted three underground nuclear tests and has fired dozens of missiles in very public tests, usually in the direction of Japan. He also claims to have chemical and biological weapons.

In addition his regime has enraged public opinion by its treatment of American college student Otto Warmbier, arrested in 2016 in North Korea for trivial offences; he was sentenced to 15 years hard labour and was last month returned home to Ohio comatose, where he died six days later.

North Korea has fired rockets across the South Korean border, launched a cyber attack on American film studio Sony Pictures and tortured high-ranking officials, including members of Kim's own family.

Kim, who is believed to be 34, is the youngest head of state in the world and frequently considered to be unhinged. He smokes, drinks and eats excessively and enjoys basketball, football, video games and racing sports cars. He also has a keen interest in military affairs.

His personality now influences every aspect of his people's lives: for example anyone else with the name 'Jong-un' has been forced to change it.

On Friday, Trump met in Washington with South Korean President Moon Jae-in. Speaking alongside Moon at the White House he declared that US patience with the North Korean regime "is over".

As The Day went to press, last night's phone calls were being seen as a severe ratcheting up of tension. Could Trump be planning military action?

Word Watch

Yes, many say. It was confirmed last week that revised US military options for North Korea have been prepared and are ready to be presented to President Trump at a moment's notice.

But they will not be used, say others. America cannot possibly move without support from the region's biggest player, China. And the Chinese will always veto any resolution put to the UN Security Council for military action against North Korea.

Stalinist: Associated with communism and the cult of the leader's personality in totalitarianism. Josef Stalin led the Soviet Union 1929-53.

Prison camps: The data on North Korea's prison population is from a 2014 UN report.

Death toll: The lower estimate was made by Marcus Noland of the Peterson Institute of International Economics; the higher estimate by Medecins Sans Frontieres researcher Fiona Terry.

34: Kim was born on January 8th in 1982, 1983 or 1984. He is the youngest of Kim Jong-il's three sons; his brothers fell out of favour before his father's death.

Military affairs: He attended the Kim Il-sung military academy from the year 2000.

Ballistic missile: A missile which is launched high into the air, and guided for a short amount of time before allowing gravity and air resistance to help it reach its target. North Korea is believed to have thousands of missiles with varied ranges, although none could reach the USA. The US Congress also estimates that North Korea has 10-16 nuclear weapons. But a Chinese estimate published in 2015 puts the number at 40 by 2016 and 100 by 2020.