US President Donald Trump says he has fired his National Security Adviser John Bolton.
"I informed John Bolton last night that his services are no longer needed at the White House," he wrote.
"I disagreed strongly with many of his suggestions," Mr Trump wrote, adding that a new national security adviser would be appointed next week.
The firing comes after Mr Bolton argued with Mr Trump over the administration's peace talks with the Taliban.
Mr Bolton, who had served since April 2018, was Mr Trump's third national security adviser after Michael Flynn and HR McMaster.
White House press secretary Stephanie Grisham told reporters: "[The president] didn't like a lot of his policies, they disagree."
She said the president asked for Mr Bolton's resignation on Monday night, and it was delivered on Tuesday morning.
What is Bolton saying?
But moments after Mr Trump's tweet, Mr Bolton took to Twitter to claim he had actually offered his resignation, but Mr Trump had told him "let's talk about it tomorrow".
As the news broke, Mr Bolton texted a Fox New host live on TV.
"John Bolton just texted me, just now, he's watching. He said, 'let's be clear, I resigned,'" Brian Kilmeade told viewers.
In separate tweets with Washington Post reporter Robert Costa, Mr Bolton maintained he had tendered his resignation on Monday night.
"I will have my say in due course," he said, adding "my sole concern is US national security".
Just two hours before his departure was announced, Mr Bolton had been due to host a White House briefing with Secretary of State Mike Pompeo and Treasury Secretary Steven Mnuchin.
The new acting national security adviser will be Charles Kupperman, who was a deputy to Mr Bolton, the White House told the BBC.
What are White House sources saying?
Sources said that the National Security Council, which advises the president, had become a separate entity within the White House under Mr Bolton.
A former senior Trump administration official, who wished to remain anonymous, told the BBC: "He [Bolton] operates separately from the rest of the White House.
According to the official, Mr Bolton did not attend meetings, and followed his own initiatives.
"He's running his own show," said the official.
A White House official told the BBC's US partner, CBS News. "Bolton has his priorities. He didn't ask the president 'What are your priorities.' They're Bolton's priorities."
A former senior administration official told CBS that Mr Bolton's "his way or the highway" approach infuriated many people inside the White House, including the president.
The anonymous source said the former national security adviser had "got too big for his britches" and "doesn't play well in the sandbox".
In the past month, a source familiar with the situation told CBS the White House drumbeat to oust Mr Bolton grew louder.
Source say it was known at the White House over the past two weeks was that Mr Bolton was on "thin ice" and he would be "the next one removed".
BBC White House reporter Tara McKelvey says she once asked Mr Bolton about his relationship with the president, and the national security adviser simply burst out laughing.
An untenable situation
John Bolton was always an unusual fit in the Trump White House. While he was an animated personality on Fox News – clearly endearing him to the president – he was also an outspoken foreign policy hawk working for a man who campaigned against international adventurism.
Mr Bolton was a strong supporter of the Iraq War, for instance, while the president has called the conflict one of the greatest US military blunders.
On topics like North Korea and Russia, the president's conciliatory position when Mr Bolton arrived in April 2018 was clear – and clearlRead More – Source