WASHINGTON — Charging ahead with the dramatic remaking of his White House, President Donald Trump said Thursday he would replace National Security Adviser H.R. McMaster with the former U.N. Ambassador John Bolton, a foreign policy hawk entering a White House facing key decisions on Iran and North Korea.

After weeks of speculation about McMaster’s future, Trump and the respected three-star general put a positive face on the departure, making no reference to the growing public friction between them. Trump tweeted Thursday that McMaster had done “an outstanding job & will always remain my friend.” He said Bolton will take over April 9 as his third national security adviser in just over a year.

The national security shake-up comes as the president is increasingly shedding advisers who once eased the Republican establishment’s concerns about the foreign policy and political novice in the White House. McMaster is the sixth close adviser or aide to announce a departure in a turbulent six weeks, joining ally Secretary of State Rex Tillerson, who was unceremoniously fired last week.

The White House has said the president is seeking to put new foreign policy leaders in place ahead of not-yet-scheduled meeting with North Korean leader Kim Jong Un. Bolton is likely to add a hard-line influence to those talks, as well as deliberations over whether to pull out of the Iran nuclear deal.

The White House said Thursday that McMaster’s exit had been under discussion for some time and stressed it was not due to any one incident, including this week’s stunning leak about Trump’s recent phone call with Russian President Vladimir Putin when Trump went against his staff’s advice and congratulated the Russian leader on his re-election.