After a Chinese envoy arrived in South Korea, the two sides have agreed to take "strong action" against North Korea if the North continues to test nuclear and ballistic missiles, according to VOA News.

Joel Witt, the cofounder of 38 North, a website that brings together experts on North Korea, told Business Insider that the country's progress in developing nuclear and ballistic missiles had appeared to rapidly increase over the past year.

With each test, North Korea gets closer to its goal of creating an intercontinental ballistic missile that could threaten the US mainland. US President Donald Trump's administration has been clear it is open to taking military action to try to prevent this.

Trump, in an interview with the Financial Times before his meeting last week with Chinese President Xi Jinping, said "