US President Donald Trump announced on Thursday that he was appointing John Bolton, a hawk who has advocated using military force against North Korea and Iran, as his national security adviser, replacing H.R. McMaster. The move, announced in a tweet and a White House statement, came little more than a week after Trump fired Rex Tillerson as secretary of state and nominated Central Intelligence Agency Director Mike Pompeo to replace him. The White House said Trump and McMaster had “mutually agreed” that he would leave. “I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend,” Trump’s tweet said. “The two have been discussing this for some time. The timeline was expedited as they both felt it was important to have the new team in place, instead of constant speculation. This was not related to any one moment or incident, rather it was the result of ongoing conversations between the two,” a senior White House official said. McMaster, 55, is to stay on until mid-April. He said in a statement he was also requesting retirement from the US Army, in which he holds the rank of three-star general. Chief of Staff John Kelly and Defense Secretary Jim Mattis had been pushing Trump to get rid of McMaster and had been escalating their campaign in recent weeks. It had appeared McMasters departure was imminent last week — but White House officials insisted the speculation was false. McMaster never developed a personal rapport with Trump, who chafed at his long-winded briefing style, according to a White House official and a person close to the president. His influence in high-level decision-making had waned in recent months, as Trump has increasingly relied on the direct counsel of Kelly and Mattis. The news of Bolton’s appointment followed a meeting he had with Trump in the Oval Office. Even Bolton was caught by surprise. “I didn’t really expect an announcement this afternoon, but it’s obviously a great honor,” he told Fox News after the announcement. “I’m still getting used to it.” Bolton, 69, is a Fox News analyst who contemplated a run for the Republican presidential nomination in 2016. He is a familiar figure in Washington, with a walrus-like moustache and hard-charging views on many global challenges. Bolton, probably the most divisive foreign policy expert ever to serve as UN ambassador, has been a force in Republican foreign policy circles for decades. He has served in the Republican administrations of Ronald Reagan, George H.W. Bush and George W. Bush, and served as a Bush lawyer during the 2000 Florida recount. The shake-up shows Trump, in office for 14 months, surrounding himself with advisers more likely to agree with his views and taking his foreign policy in a more hawkish direction. What it means for a prospective summit meeting between Trump and North Korean leader Kim Jong Un is unclear. The meeting is supposed to happen by the end of May, but an exact time and place have yet to be settled on. Bolton’s appointment could doom the already endangered Iran nuclear deal. It could also lead to friction with Trump on how tough to be on Russia, with the president still holding out hope for improved ties with Russian President Vladimir Putin. Some members of Congress immediately questioned his selection for the critical position in the White House. “This is not a wise choice. Mr. Bolton does not have the temperament or judgment to be an effective national security adviser,” Democratic Senator Jack Reed said in a statement. Bolton tweeted on January 11 that time was running out on stopping North Korea’s nuclear weapons program. He said: “We’ve got to look at the very unattractive choice of using military force to deny them that capability.” At a time when Trump has threatened to withdraw the United States from the 2015 Iran nuclear deal, unless Europe agrees to change it, Bolton has tweeted that the deal “needs to be abrogated.” He has also called for “effective countermeasures to the cyber war that Russia is engaging.”