File photo taken on Nov. 2, 2017 shows H.R. McMaster speaks at a press briefing at the White House in Washington D.C., the United States. U.S. President Donald Trump tweeted on March 22, 2018 that John Bolton, former U.S. Ambassador to the United Nations, will replace General H.R. McMasterto be his new national security adviser. (Xinhua/Yin Bogu)

WASHINGTON, March 22 (Xinhua) -- U.S. President Donald Trump tweeted on Thursday that John Bolton, former U.S. Ambassador to the United Nations, will replace General H.R. McMaster to be his new national security adviser.

Trump added that the announcement will be effective on April 9, when there will be an official contact handover.

"I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend," Trump said.

Later, U.S. Ambassador to the United Nations Nikki Haley also tweeted that McMaster's "selfless courage and leadership has inspired all of us. Most of all, thank you for your friendship."

The Washington Post reported last week that Trump has decided to sack McMaster, and was "actively" talking about potential replacements.

Richard Hass, president of the U.S. think tank Council on Foreign Relations, questioned Bolton's qualifications.

"A national security advisor must be an honest broker, ensuring the Potus considers all points of view. Second, he is a counselor with his own views... the obvious question is whether John Bolton has the temperament and the judgment for the job," Hass noted.

Bolton, born in 1949, has served the Reagan and Bush administrations. He has been largely known for his hawkish stance. He also strongly lashed out at the United Nations, threatening not to pay for the U.S. dues if his requirements were not met.

Trump was said to be "comfortable" with firing McMaster, with whom he has never had personal chemistry.

He has also complained that McMaster's briefings went on too long and seemed irrelevant, according to reports.

As McMaster has "been on thin ice for months," Trump was said to be willing to take time implementing the move so as to ensure McMaster does not feel "humiliated" and that there is a strong successor to replace him.

Although Sarah Sanders, the White House spokesperson, later tweeted that Trump and McMaster "have a good working relationship" and there were no changes at the National Security Committee, Trump has reportedly told White House Chief of Staff John Kelly to help him weigh on replacement options.

Thursday's change of personnel marked yet another shakeup in the senior ranks of the Trump administration. Trump earlier announced to fire State Secretary Rex Tillerson, replacing him with Mike Pompeo, the current chief of Central Intelligence Agency.

John McEntee, Trump's longtime personal aide, was forced out of the White House after his security clearance was abruptly revoked.

Trump recently nominated former TV analyst Larry Kudlow to replace Gary Cohn, his top economic adviser that quit over tariff disagreements with Trump.

Trump was also reportedly considering replace Veterans Affairs Secretary David Shulkin with Energy Secretary Rick Perry. Shulkin has ruffled Trump's feathers for his extravagant spending habit and pervasive disorder inside his agency.

Other cabinet personnel on the U.S. media's watch list included Education Secretary Betsy DeVos, who has shown a clear lacking of preparation in attending CBS's "60 Minutes;" Housing and Urban Development Secretary Ben Carson, who has created headlines for ordering a dining room set for his office worthy of 31,000 U.S. dollars; Environmental Protection Agency Administrator Scott Pruitt, traveling in first-class cabins at taxpayer's expense; and Interior Secretary Ryan Zinke, who spent 139,000 U.S. dollars to renovate his office doors.