WASHINGTON (Reuters) - President Donald Trump is considering a plan to oust Secretary of State Rex Tillerson, whose relationship has been strained by the top U.S. diplomat’s softer line on North Korea and other differences, senior administration officials said on Thursday.

Tillerson would be replaced within weeks by CIA Director Mike Pompeo, a Trump loyalist and foreign policy hard-liner, under a White House plan to carry out the most significant staff shake-up so far of the Trump administration.

Republican Senator Tom Cotton, one of Trump’s staunchest defenders in Congress, would be tapped to replace Pompeo at the Central Intelligence Agency, the officials told Reuters, speaking on condition of anonymity.

It was not immediately clear whether Trump had given final approval to the reshuffle, but one of the officials said the president asked for the plan to be put together.

Tillerson’s long-rumored departure would end a troubled tenure for the former Exxon Mobil Corp chief executive, who has been increasingly at odds with Trump over issues such as North Korea and under fire for planned cuts at the State Department.

Tillerson was reported in October to have privately called Trump a “moron,” something the secretary of state sought to dismiss.

That followed a tweet by Trump that Tillerson should not waste his time by seeking negotiations with North Korea over its nuclear and missile program, widely seen as a sign of the secretary of state being marginalized.

Trump has soured on Tillerson mostly because of the “moron” report, his less confrontational approach on North Korea and differences over the Qatar crisis, one senior U.S. official said.

His slow approach to filling diplomatic openings at the State Department is also a factor, another official said.

Trump asked John Kelly, the White House chief of staff, to develop the transition strategy, and it has been discussed with other officials, one administration source said.

Under the plan, which has been in the works for weeks and was first reported by the New York Times, the reshuffle would happen around the end of the year or shortly afterward, the official said.

Asked whether he wanted Tillerson to remain in his job, Trump sidestepped the question, telling reporters at the White House: “He’s here. Rex is here.”

State Department spokeswoman Heather Nauert said Kelly told Tillerson’s chief of staff on Thursday the reports on Tillerson being replaced were not true. Nauert added that Tillerson “serves at the pleasure of the president.”

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Asked about Tillerson, White House spokeswoman Sarah Sanders said the secretary of state remained in his post. “When the president loses confidence in someone, they will no longer serve here,” she said.

Pompeo, a former congressman, has moved to the forefront as he has gained Trump’s trust on national security matters.

Tillerson, 65, has spent much of his tenure trying to smooth the rough edges of Trump’s unilateralist “America First” foreign policy, with limited success. On several occasions, the president publicly undercut his diplomatic initiatives.

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A source familiar with Tillerson’s thinking said the secretary of state’s original plan when he took the job was to leave in February.

If carried out, the staff changes would be the latest in a string of firings or resignations in the Trump administration including the departures of the chief of staff, national security adviser and FBI director.

FOREIGN POLICY HARDLINER

Pompeo, 53, has taken tough foreign policy stands, especially on Iran, and talked about how his agency is becoming more aggressive and how he has been focusing on deploying more CIA officers overseas.

He has offered effusive praise for Trump despite the president’s criticism of U.S. intelligence agencies, some of which concluded that Russia conducted an influence campaign to boost Trump in the 2016 presidential election.

Tillerson has at times put distance between himself and Trump’s positions.

At a private dinner of foreign policy veterans last month, a senior White House official criticized Tillerson for failing to support the president’s agenda, according to a person familiar with the matter.

Tillerson joined Defense Secretary Jim Mattis in pressing Trump not to pull the United States out of an agreement with Iran and world powers over Tehran’s nuclear capabilities.

Tillerson has taken a more hawkish view than Trump on Russia and tried to mediate a dispute after four Arab nations launched a boycott of Qatar.

In September in Beijing, Tillerson said Washington was probing North Korea to see whether it was interested in dialogue, and had multiple direct channels of communication with Pyongyang.

The next day, Trump appeared to dismiss those efforts in a tweet, telling Tillerson he was “wasting his time.”

Tensions have also run high between Tillerson and veteran diplomats who oppose his proposed staff and budget cuts.