Sources reportedly said Melania explicitly called for the ousting of the aide, after the pair's dealings regarding her recent trip to Africa "didn't go well".
Trump has been mulling removing Nielsen, a Kelly protege who became the secretary at Homeland Security when he left the job to become Trump's chief of staff, for a number of weeks, a source told Reuters news agency.
The announcement could come as soon as this week, the officials said.
Mattis declined to comment when asked about the staffing changes by Pentagon reporters.
The remark is uncharacteristically harsh for the first lady, but there's a backstory.
Ricardel, Bolton's top deputy, clashed with the first lady's staff after threatening to withhold National Security Council resources during Melania Trump's trip to Africa last month unless Ricardel or another NSC official was included in her entourage, one person familiar with the matter said.
"This will be our fourth secretary in two years", the official said. The deputy secretary job at DHS has been vacant since February, and the White House has not submitted to Congress a nomination for that post.
BMW M340i Emerges Just Shy Of A Full-On M3
Finally, you get some lovely blue paint plus M logos to finish off the four-piston front/single piston rear brake calipers. Since the M340i sits among the regular model line-up, it does without muscle flexing features like flared arches.
13 hidden North Korean missile bases outed in new report
Located 135 kilometers north of the South Korean capital of Seoul, it can reach the city in a short period of time, it said.
David Schwimmer lookalike arrested for 'stealing cans of lager' in Blackpool
As many fans pointed out last month via Blackpool Police's Facebook page, the theft suspect looks nearly identical to Schwimmer. Lancashire Police posted a tweet today saying that they'd arrested a 36-year-old man in London yesterday on suspicion of theft.
A White House official accused Ricardel of being dishonest about the feud and subsequently leaking stories to try to cover her behavior. Homeland Security is responsible for protecting the country's borders and enforcing immigration laws. The last thing we want is someone who needs hand-holding'.
The Post, citing five unnamed sources, said that Trump has been unhappy with Nielsen's performance and canceled a planned visit to US armed forces at the border with Mexico.
The Washington Post reported on Monday that Nielsen's departure, although not yet finalized, is imminent. Kelly 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.
But sources say she could fall victim to the president's frustration that his immigration agenda has stalled.
If they leave, Kelly and Nielsen would join a long list of people who have been fired by Trump or resigned since he took office in January, 2017.