- A replacement -- the White House's fourth national security chief in less than three years -- would be named next week, Trump said.
- Bolton is a veteran and controversial figure closely linked to the invasion of Iraq and other aggressive US foreign policy decisions.
- He joins a stack of senior officials to have come and gone during the Republican businessman's tumultuous first term in office.
President Donald Trump on Tuesday announced the firing of hawkish national security advisor John Bolton, a move widely seen as boosting the president's push to negotiate with US foes in Afghanistan, North Korea and other trouble spots.
Trump, who said he had disagreed "strongly" with Bolton on policy, announced via Twitter: "I asked John for his resignation, which was given to me this morning."
A replacement -- the White House's fourth national security chief in less than three years -- would be named next week, Trump said.
Bolton, who had been scheduled to give a press conference at the White House on an unrelated matter, denied being fired and insisted that he had resigned.
The news, coming days after Trump caused uproar by revealing he was cancelling secret talks with Afghanistan's Taliban, stunned Washington.
Bolton is a veteran and controversial figure closely linked to the invasion of Iraq and other aggressive US foreign policy decisions.
He had been seen as one of the main driving forces in the White House's muscular approach to Iran, North Korea, Venezuela and elsewhere.
Famous for his large moustache and ever-present yellow legal pad, the hardline former US ambassador to the United Nations had pushed back against Trump's dramatic, though so far stumbling, attempts to negotiate with the Taliban and North Korean leader Kim Jong Un.
According to US media reports Trump's extraordinary but failed bid to fly Taliban leaders into the presidential retreat at Camp David last weekend sparked a major, final row.
Secretary of State Mike Pompeo cautioned that Bolton's exit should not be interpreted as heralding strategy changes.
"I don't think any leader around the world should make any assumption that because someone of us departs that president Trump's foreign policy will change in a material way," Pompeo told reporters.
Treasury Secretary Steven Mnuchin underlined that Trump and top aides remain "completely aligned" on Washington's crippling sanctions against Iran, known as the maximum pressure campaign.
But when asked if Trump was still open to meeting his Iranian counterpart Hassan Rouhani at the United Nations General Assembly this month -- an event that would be as ground breaking as his proposed Taliban talks -- Pompeo said "sure."
As so often in the Trump presidency, the handling of the abrupt reshuffle appeared chaotic.
Bolton joins a stack of senior officials to have come and gone during the Republican businessman's tumultuous first term in office.
Since entering the White House in January 2017, Trump has had two secretaries of defense, as well as two acting secretaries, two secretaries of state, two CIA directors and a half dozen communications directors.