WASHINGTON (WASHINGTON POST) - US President Donald Trump has told advisers he has decided to remove Homeland Security Secretary Kirstjen Nielsen and her departure from the administration is likely to occur in the coming weeks, if not sooner, according to five current and former White House officials.

Mr Trump cancelled a planned trip with Ms Nielsen this week to visit US troops at the border in south Texas and told aides over the weekend he wants her out as soon as possible, these officials said.

The President has grumbled for months about what he views as Ms Nielsen's lacklustre performance on immigration enforcement and is believed to be looking for a replacement who will implement his policy ideas with more alacrity.

The announcement could come as soon as this week, three of these officials said.

Mr Trump has changed his mind on key personnel decisions before and Chief of Staff John Kelly is fighting Ms Nielsen's pending dismissal and attempting to postpone it, aides say.

But General Kelly's future in the administration is also shaky, according to three White House officials.

A spokesman for the Department of Homeland Security declined to comment on Ms Nielsen's potential departure.

Ms Nielsen has been reluctant to leave the administration before reaching the one-year mark as secretary on Dec 6, but she has been unhappy in the job for several months, according to colleagues.

Mr Trump has berated her during Cabinet meetings, belittled her to other White House staff and tagged her months ago as a "Bushie", a reference to her previous service under former US president George W. Bush and meant to cast suspicion on her loyalty.

As she has tried to explain the laws and regulations that prevent the government from drastically curtailing immigration or closing the border with Mexico - as Mr Trump has suggested - the President has grown impatient and frustrated, aides said.

Her departure would leave a leadership void at the government's third-largest agency, which has 240,000 employees and a US$60 billion (S$82.9 billion) budget.

The deputy secretary job at the Department of Homeland Security has been vacant since February and the White House has not submitted to Congress a nomination for that post.

Unless Mr Trump were to name another official to lead the Department of Homeland Security in an acting capacity, the day-to-day task of running the agency would fall to Ms Claire Grady, the undersecretary for management.

Mr Trump has told White House officials that he has begun contemplating replacements for Ms Nielsen. He could name one of the agency's other Senate-confirmed principals, such as Mr Kevin McAleenan, commissioner of US Customs and Border Protection, or Mr David Pekoske, administrator of the Transportation Security Administration and a former vice-commandant of the Coast Guard.

"If I were advising the White House, I'd encourage them to nominate someone with executive branch experience," said a senior Department of Homeland Security official, who spoke on the condition of anonymity. "This will be our fourth secretary in two years. The last thing we want is someone who needs hand-holding."

Mr Kris Kobach's loss in the Kansas governor's race has generated speculation that Mr Trump could attempt to nominate him as a replacement for Ms Nielsen, but Mr Kobach, Kansas' secretary of state, remains a polarising figure whose hardline views - especially on immigration - are considered by many observers to be too extreme to win Senate confirmation.

Colleagues who have worked closely with Ms Nielsen and defend her performance at the Department of Homeland Security say working for Mr Trump on immigration issues is miserable because the President has an unrealistic view of border security and little patience for the intricacies of US immigration law.

Ms Nielsen was selected for the job by Gen Kelly and her imminent departure is another indication that his influence over staff and personnel decisions has waned.

He has defended her repeatedly and aides have grown annoyed at their close relationship - he often praises her impromptu in senior staff meetings while not praising other Cabinet members.

Former colleagues who worked with Ms Nielsen were astonished when he pushed to install her at the Department of Homeland Security because she had never led a large organisation, let alone one with so many responsibilities.

She worked on disaster management response in the Bush White House, then in the private sector and academia as a cyber security expert before returning to the Department of Homeland Security to work as chief of staff under Gen Kelly when he was Homeland Security secretary during Mr Trump's first six months in office.

But it was immigration enforcement that became one of Mr Trump's biggest frustrations and he has blamed her for a rebound this year in the number of people arrested along the Mexico border.

At the peak of controversy over the Trump administration's "zero tolerance" family-separation initiative, Ms Nielsen nonetheless stood at the White House lectern and delivered a vigorous defence of the measures.

The President loved her performance - especially when she said there was no administration policy on separations.

Days later, under withering criticism, the President changed his mind and ordered an end to the separations.