Steve Bannon, President Donald Trump's chief strategist, has lost his seat on the powerful National Security Council (NSC) in a high-level shakeup, US officials said on Wednesday.

Trump's elevation of Bannon to a permanent spot on the NSC had been widely criticised as injecting politics into White House deliberations on sensitive defence, foreign policy, and intelligence matters.

A former head of the right-wing website Breitbart and now chief White House strategist, Bannon is regarded as a controversial proponent of the nationalistic anti-globalism that helped propel Trump to the White House last November.

In a presidential memo dated April 4, Bannon no longer appears on the list of regular attendees of NSC meetings.

"[Bannon's removal is] striking because many people believed he shouldn't have been there in the first place, and that he was there at the expense of two key roles being removed … the director of national intelligence as well as the joint chiefs," Al Jazeera's Kimberly Halkett said, reporting from outside the White House.

A senior White House official told The Associated Press on Wednesday that Bannon was initially placed on the NSC after Trump's inauguration as a measure to ensure implementation of the president's vision, including efforts to downsize and streamline operations at the council.

'Key ideologist'

Hillary Mann Leverett, the CEO of Stratega, a political risk consultancy, said it remains to be seen what role Bannon, who joined Trump's team late in the presidential campaign, will have going forward.

"He was perceived as decisive for the Trump victory but it's not like these two men have a deep, long-standing relationship," she told Al Jazeera.

Mann Leverett said Bannon's main contribution to Trump's team was a coherent ideology - one many would disagree with, but that proved popular with voters especially in rural states where many jobs have been lost.

"Bannon had a very focused, coherent strategy, both in terms of domestic politics and in terms of the idea of 'America First' and how the United States should position itself on the international stage," she said.

"Not many other people around Trump have such a coherent, focused ideology and agenda... so he does provide unique advice to the president but it's not necessarily the one the president thinks is the winning piece of advice going forward."

Trump's first national security adviser, Michael Flynn, was at the helm of the NSC at the time, but the official said Bannon's role on the committee had nothing to do with the troubles facing Flynn, who was later asked to resign for misleading the administration about his communication with Russian officials.

The new memo also restores the director of national intelligence and the Joint Chiefs chairman to the principals committee.

Bannon's addition to the NSC sparked concerns from Trump critics, who said it was inappropriate for the political adviser to play a role in national security matters.