Through Twitter on Tuesday, U.S. President Donald Trump announced that he had asked U.S. National Security Advisor John Bolton for his resignation, informing him that "his services are no longer needed at the White House."
The U.S. president added that he "disagreed strongly with many of his suggestions", as did others in the Trump administration.
Trump will be naming a new National Security Adviser next week.
The latest announcement comes after months of rumors that the two clashed on policy, including on how to denuclearize North Korea.
Some of their disagreements were openly seen in public, with Trump playing down North Korea's short-range ballistic missile tests, while Bolton called them out as violations of UN Security Council resolutions.
During a press conference at the White House on Tuesday, U.S. Secretary of State Mike Pompeo said he was not surprise by the news, adding that there were also times when he, too, had his differences with Bolton.
There were many times Ambassador Bolton and I disagreed. That's to be sure. But that's true for lots of--, lots of people with whom I interact.
Bolton was appointed as Trump's third national security adviser in April last year, and was known for his hawkish views on regimes such as North Korea, Iran and Venezuela.
He's also widely known to have advised Trump to walk out of the second summit with North Korean leader Kim Jong-un in Hanoi back in February, after Pyeongyang offered to dismantle only its main nuclear facility in Yongbyon.
Meanwhile according to Harry Kazianis, a senior director at the Center for the National Interest, a new national security adviser will be picked from a large pool of potential candidates, but U.S. Special Representative for North Korea Stephen Biegun, who's been leading the negotiations for denuclearization talks, could be a strong choice.
Watchers say Bolton's removal from the administration could have implications for North Korea-U.S. denuclearization talks, as Pyeongyang offered to resume talks with Washington in late September.
If held, the meeting would mark the first formal negotiations since the breakdown of the Hanoi summit.
Lee Seung-jae, Arirang News.