US military action against North Korea is an "option on the table", Secretary of State Rex Tillerson has said.

Donald Trump's highest-ranking foreign policy advisor said that he would bring an end to the policy of "strategic patience", where the US tolerates nuclear tests and missiles from the country, he said during a visit to South Korea. Instead, the US will explore a range of military options, alongside diplomatic, security and economic measures.

The statement marks a major change from the US's policy on North Korea, which has tended to see it criticise but not necessarily respond to hostile actions by North Korea.

Tensions are rising between North and South Korea after a range of tests initiated by the North. It has recently boasted of firing a missile into the sea and has promised to test more weapons in the future.

Mr Tillerson said that any North Korean actions that threatened the South would be met with "an appropriate response".

He said said that the US does "not want to, for things to get to military conflict". But he said that if North Korea "elevate the threat of their weapons programme to a level that we believe requires action, then, that option's on the table".

Mr Tillerson made the comments after a tour of the demilitarised zone between the two countries. He had earlier vowed that the US would be tougher on North Korea's nuclear threat, but didn't give any details on what that "different approach" would consist of.

He pointedly noted that 20 years of "diplomatic and other efforts" had failed to dissuade the isolated communist government from developing its nuclear program, which he called an "ever-escalating threat."

Inside the daily life in North Korea Show all 19 1 /19 Inside the daily life in North Korea Inside the daily life in North Korea People reading a newspaper at the metro station Inside the daily life in North Korea Thoughts of the leaders on the tram. They have about a dozen of these on every tram, all with different thoughts Inside the daily life in North Korea Young people training for a big upcoming festival Inside the daily life in North Korea People at the Pyongyang's annual marathon Inside the daily life in North Korea Many stars on one of the trolleys in Pyongyang Inside the daily life in North Korea An intimidating poster in a primary school in North Korea. Inside the daily life in North Korea Solar panels installed on a street lamp. Inside the daily life in North Korea A poster on the window next to one of the venues we visited in Pyongyang Inside the daily life in North Korea Kids playing football next to the Arch of Triumph. After a while tourists were allowed to join, so some of us did Inside the daily life in North Korea Class in an educational center in Pyongyang (where people over 17 years old can attend any classes they choose after school, for free) Inside the daily life in North Korea People waving at me during the Pyongyang marathon Inside the daily life in North Korea People having a great time dancing at a public park Inside the daily life in North Korea A metro driver in a metro station in Pyongyang Inside the daily life in North Korea Fireworks to mark the birthday of the Eternal President Kim Il Sung on our last night in Pyongyang Inside the daily life in North Korea My wonderful tour guide at a public park Inside the daily life in North Korea One of the parks in Pyongyang Inside the daily life in North Korea A person rowing some boats for the day at a river in Pyongyang Inside the daily life in North Korea The National War Museum Inside the daily life in North Korea Public park in Pyongyang

Tensions between North and South Korea come as military exercises become commonplace more generally in the region. Donald Trump's closest advisor has predicted that there will be a war between the US and China in the next few years.

Mr Tillerson called on China to take on North Korea, by implementing sanctions. And he said that the country does not need to punish South Korea, which it is doing for deploying a US anti-missile system that is intended to help it defend against North Korea.

China has called that system – the Terminal High Altitude Area Defense (THAAD) – a threat to its own security and penalised South Korea for allowing it to be built.

"We believe these actions are unnecessary and troubling," Tillerson said, referring to what South Korea sees as Chinese retaliation in the form of business restrictions in response to the deployment of the missile system.

"We also believe it is not the way for a regional power to help resolve what is a serious threat for everyone. So we hope China will alter its position on punishing South Korea."

"We hope they will work with us to eliminate the reason THAAD is required."

China resents U.S. pressure to do more on North Korea and says it is doing all it can but will not take steps to threatened the livelihoods of the North Korean people.

China has urged North Korea to stop its nuclear and missile tests and said South Korea and the United States should stop joint military exercises and seek talks instead.

Chinese state media reiterated on Friday that the main problem was between the United States and North Korea, and denounced what it called the "throwing of dirty water" at China by Washington and Seoul.