President Trump fired John R. Bolton, his third national security adviser, on Tuesday amid fundamental disagreements over how to handle major foreign policy challenges like Iran, North Korea and Afghanistan.

Mr. Trump announced the decision on Twitter. “I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week.”

President Trump fired John R. Bolton, his third national security adviser, on Tuesday amid fundamental disagreements over how to handle major foreign policy challenges like Iran, North Korea and Afghanistan.

Mr. Trump announced the decision on Twitter. “I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week.”