Donald Trump has accused North Korea of “behaving very badly” – and said that China has done “little to help”.

The US President said on Twitter: “North Korea is behaving very badly. They have been ‘playing’ the United States for years. China has done little to help!”

His words came as US Secretary of State Rex Tillerson said military action against North Korea was an “option on the table”.

The President’s highest-ranking diplomat said during a visit to South Korea that he would bring an end to the policy of “strategic patience”, where the US tolerated the North’s nuclear and missile tests.

Instead, he said, the US would explore a range of military options, alongside diplomatic, security and economic measures.

The statement marks a major change from the US’s policy on Pyongyang, which has tended to see it criticise but not necessarily respond to hostile actions by Kim Jong-un’s regime.

Mr Tillerson made his remarks in Seoul after visiting the buffer zone between the two countries. The area is said to be the most heavily armed border in the world.

US military action against North Korea 'an option on the table'

He outlined a tougher strategy to confront North Korea’s nuclear threat and said he was not interested in talks with Pyongyang unless it started the process of giving up its nuclear weapons.

Asked about the possibility of using military force, Mr Tillerson told reporters “all of the options are on the table”.

The Secretary of State met with his South Korean counterpart Yun Byung-se and the country’s acting President, Hwang Kyo-ahn, on the second leg of a three-nation trip which began in Japan and will end in China. The Associated Press said US State Department officials have described it as a “listening tour” as the administration seeks a coherent North Korea policy.

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On his final day in office, Barack Obama was reported to have told Mr Trump that dealing with North Korea would likely be his most pressing challenge once he assumed office.

North Korea has successfully launched hundreds of short- and mid-range missiles, but it has not yet launched a long-range missile that might threaten the US.

However, North Korea’s leader recently said the country will soon test intercontinental missiles. Experts have said it is difficult to know if he is bluffing or telling the truth.

During the presidential campaign, Mr Trump frequently voiced concerns about North Korea’s nuclear programme and called on China to use its influence to deal with the situation.