U.S. President Donald Trump abruptly fired his national security adviser, John Bolton, amid disagreements with his hard-line aide over how to handle foreign policy challenges such as the Democratic People's Republic of Korea (DPRK), Iran, Afghanistan and Russia. 

"I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration," Trump tweeted on Tuesday, adding that he would name a replacement next week.

Bolton, a leading foreign policy hawk and Trump's third national security adviser, had pressed the president not to let up pressure on the DPRK despite diplomatic efforts. 

The chief architect of Trump's strident stance against Iran had also argued against Trump's suggestions of a possible meeting with the Iranian leadership and advocated a tougher approach on Russia and, more recently, Afghanistan. 

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The announcement followed an acrimonious conversation on Monday that included their differences over Afghanistan, said a source familiar with the matter.

The 70-year-old Bolton, who took up the post in April 2018, replacing H.R. McMaster, had also often been at odds with Secretary of State Mike Pompeo, a Trump loyalist.

Offering a different version of events than Trump, Bolton tweeted: "I offered to resign last night and President Trump said, 'Let's talk about it tomorrow.'"

Stephen Biegun, special U.S. envoy on the DPRK, is among the names that have been floated as possible successors. 

"Biegun is much more like Pompeo, (he) understands that the president is the president, that he makes the decisions," said a source close to the White House. 

Also considered in the running is Deputy Secretary of State John Sullivan, who had been expected to be named U.S. ambassador to Russia, and Richard Grenell, U.S. ambassador to Germany, people familiar with the matter said. 

White House spokeswoman Stephanie Grisham said "many, many issues" led to Trump's decision to ask for Bolton's resignation. She would not elaborate.

U.S. Secretary of State Mike Pompeo told reporters at the White House: "... I don't think that any leader around the world should make any assumption that because some one of us departs that President Trump's foreign policy will change in a material way... There were many times Ambassador Bolton and I disagreed, that's to be sure, but that's true for lots of people with whom I interact."

Republican senators had a mixed response. Mitt Romney of Utah said it was "an extraordinary loss for our nation and for the White House," while Rand Paul of Kentucky said "the threat of war worldwide goes down exponentially" with Bolton out. 

Iranian government spokesman Ali Rabiei wrote on Twitter: "John Bolton had promised months ago that Iran would last for another three months. We are still standing and he is gone. With the expulsion of the biggest proponent of war and economic terrorism, the White House will face fewer obstacles in understanding Iran's realities."

Norbert Roettgen, chairman of the foreign policy commission of the German parliament and senior lawmaker from German Chancellor Angela Merkel's Christian Democratic Union party, said that this is an opportunity, not least for the trans-Atlantic relationship, reported Reuters.

Russia does not expect its ties with Washington to suddenly improve following the exit of John Bolton, RIA news agency cited Deputy Foreign Minister Sergei Ryabkov as saying on Wednesday. 

Meanwhile, oil prices declined on Tuesday after Bolton's departure was announced.

Analysts said the news weighed on the oil market as Bolton's departure would potentially ease tensions between the United States and Iran, which would put more oil on the market. 

The West Texas Intermediate (WTI) for October delivery decreased 0.45 U.S. dollar to settle at 57.40 dollars a barrel on the New York Mercantile Exchange, and Brent crude for November delivery declined 0.21 dollar to close at 62.38 dollars a barrel on the London ICE Futures Exchange. 

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What John Bolton's departure means for U.S. foreign policy

John Bolton's exit is just the latest addition to a list of more than 60 high-ranking officials who were either sacked by the U.S. president – or chose to resign. Here's a quick look below.

(With input from Reuters, AFP, Xinhua)