WASHINGTON — U.S. President Donald Trump announced on Tuesday that he is firing his national security adviser, John Bolton, after a year and a half on the job. Trump wrote on his Twitter account that the two had disagreements over policy questions, and therefore he informed Bolton "that his services are no longer needed at the White House."

Trump added: "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."

Bolton was considered the most hawkish among Trump's senior advisers, especially regarding Iran. By firing him, Trump is moving aside the one person in his administration who would have likely opposed any kind of negotiations with the regime in Tehran.

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Trump wrote that he "disagreed strongly with many of his [Bolton's] suggestions, as did others in the Administration."

Iranian Foreign Minister Mohammad Javad Zarif constantly referred to Bolton as one of the "three B's" – three people who according to Zarif are pushing Trump towards war with Iran, Bolton, Prime Minister Benjamin Netanyahu and Saudi Arabia’s Crown Prince Mohammed bin Salman.

Within the Trump administration, Bolton was considered one of the closest people to Netanyahu and to the Israeli ambassador to Washington, Ron Dermer.

He shared Netanyahu's views regarding Iran, and was involved in the recent discussions between Israeli and American officials about some form of "gesture" to the prime minister from the administration ahead of the Israeli election next week.

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Offering a different version of events, Bolton tweeted: "I offered to resign last night and President Trump said, 'Let's talk about it tomorrow.'"

Bolton, who was Trump's third national security adviser, was also known to have pressed the president for a harder line on North Korea, Russia and Afghanistan.

Trump and Bolton were always unlikely foreign policy allies, with Bolton skeptical of Trump's outreach on North Korea and efforts to woo Russian President Vladimir Putin and supportive of an Iraq war hated by his boss.

Still, they worked together relatively smoothly for 17 months, with Bolton pressing his hawkish viewpoints behind the scenes, winning some internal debates and losing others, always pointing out that he was not the decision maker.

Two sources familiar with the matter said one thing that bothered Trump was the possibility that Bolton let it be known that Vice President Mike Pence shared his opposition to Trump's effort to bring Taliban leaders to the presidential retreat of Camp David, Maryland, to try to reach a peace deal.

The implication was that Bolton was trying to ally himself with Pence and send Trump a message that even the vice president disagreed with him, which irked the president, the sources said.

Trump had sometimes joked about Bolton's image as a warmonger, reportedly saying in one Oval Office meeting that "John has never seen a war he doesn't like."

Bolton took up the post in April 2018, replacing H.R. McMaster. He had sometimes been at odds with Secretary of State Mike Pompeo, one of Trump's main loyalists.

In May, The New York Times published quotes by a long-time aide to Bolton who claimed he secretly reviled the president, signalling to tensions in the working relationship between the two.

The article by Dexter Filkins quoted Mark Groombridge, who worked with Bolton for 15 years and advised him while Bolton served as U.S. ambassador to the United Nations under President George W. Bush, including a comment where he called Trump a "moron."

“John is thinking, 'To the extent I can modify or mollify the President’s actions, I will,'” Groombridge argued. “He is truly a patriot. But I wonder how he goes into work every day, because deep in his heart he believes the president is a moron.”

Given that "Trump does not want war," the diplomat argued Bolton must have had to work hard to convince Trump to hire him, saying, "to get the job, Bolton had to cut his balls off and put them on Trump's desk."

Reuters contributed to this report