U.S. President Donald Trump said Tuesday on Twitter that he sacked National Security Adviser John Bolton, known as a hardliner on North Korea and Iran, over disagreements on policy issues.

"I disagreed strongly with many of his suggestions, as did others in the Administration and therefore...I informed John Bolton last night that his services are no longer needed at the White House," the president said, adding that a successor will be named next week.

Bolton, meanwhile, suggested that he decided to leave the administration himself. "I offered to resign last night and President Trump said, 'Let's talk about it tomorrow,'" he tweeted.

Replacing H.R. McMaster on April 9 last year, the 70-year-old Bolton was the third national security adviser for Trump since the launch of his administration in January 2017.

Bolton reportedly had tense relations with U.S. Secretary of State Mike Pompeo, who also favors hard-line stances. The outgoing adviser was said to have been sidelined recently during sensitive discussions regarding Afghanistan policy, as the Trump administration sought a peace deal with the Taliban aimed at ending America's longest war in history.

On North Korea, Bolton had criticized the short-range ballistic missile tests carried out by Pyongyang in May as a violation of U.N. Security Council resolutions, while Trump sought to downplay the impact of such tests apparently to keep denuclearization talks alive.

Pompeo, seen as one of Trump's closest confidantes, told a press conference Tuesday that he will "leave it to the president to talk about the reasons he made the decision."

But he admitted, "There were many times Ambassador Bolton and I disagreed, that's to be sure."

Signaling the abruptness of the announcement, Bolton had been expected to participate as security adviser in the press conference at which Pompeo spoke.

Bolton was the U.S. ambassador to the United Nations from 2005 to 2006 after serving as undersecretary of state for arms control and international security from 2001 to 2005.