US President Donald Trump has named John Bolton as his new National Security Adviser, raising alarms among opposition leaders and foreign policy experts, who called the former American ambassador to the United Nations a warmonger over his record on the Iraq war and views on Iran and North Korea.

In a social media post late on Thursday, Trump announced that Bolton will replace Lieutenant General HR McMaster as his chief adviser on national security beginning on April 9.

In a statement, Bolton said he has accepted the appointment, adding that it is an "honour" to become a part of Trump's cabinet.

"The United States currently faces a wide array of issues and I look forward to working with President Trump and his leadership team in addressing these complex challenges in an effort to make our country safer at home and stronger abroad".

Bolton's appointment and McMaster's departure followed weeks of political turmoil in Washington, DC.

Last week, Trump forced out Rex Tillerson as his US Secretary of State and appointed CIA director Mike Pompeo as his replacement.

A White House source told Al Jazeera that Trump and McMaster "mutually agreed" on the decision for him to resign.

The source denied that the reshuffle was related to recent developments in Trump's cabinet, saying it was the result of "ongoing conversations" between the two officials.

In a separate statement, Trump praised McMaster's 30 years of service in the military and the government, saying "his bravery and toughness are legendary".

In confirming his resignation, McMaster also announced his retirement from the US Army.

"Throughout my career, it has been my greatest privilege to serve alongside extraordinary servicemembers and dedicated civilians."

'Too extreme'

McMaster's replacement, Bolton, is seen as a hardliner on foreign policy. As a senior official at the state department during George W Bush's administration, he led in the opposition to the creation of the International Criminal Court, and was seen as a cheerleader of the Iraq invasion.

Despite his appointment as US ambassador to the UN, he was a critic of the international body.

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Bernie Sanders, a senator and Trump critic, tore into Bolton's record, saying he was "part of the effort to mislead the US into the disastrous Iraq war, and has supported military action against North Korea and Iran".

"He was too extreme to be confirmed as UN ambassador in 2005 and is absolutely the wrong person to be national security adviser now".

Elizabeth Warren, another opposition senator, said Bolton "never met a war he didn't like".

"The last thing we need is someone like John Bolton who embraces military solutions first and puts us all at risk," she said.

On Iran, Bolton is also seen as a hawk, advocating for attacks on the country's military facilities.

In a statement following Bolton's appointment, the National Iranian American Council said, "Donald Trump may have just effectively declared war on Iran."

"Bolton is an unhinged advocate for waging World War III. He has explicitly called for bombing Iran for the past 10 years and has suggested the US engage in nuclear first strikes in North Korea," the statement said.

Bolton has also been criticised for his reported links to well-known anti-Islam individuals and groups.

He wrote the foreword to a book by Pamela Geller, who the Southern Poverty Law Center (SPLC) describes as "one of the most flamboyant anti-Muslim activists in the United States", and Robert Spencer, who the SPLC says is "one of the most prolific anti-Muslim figures in the United States".

Bolton also spoke at a 2016 American Freedom Alliance titled "Can Islam and the West Coexist?". The American Freedom Alliance is considered a "hate group" by the SPLC. In his speech, he joked that then President Obama was a Muslim.