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.
Thunder Purple OnePlus 6T will be available in the U.S
While I haven't seen Thunder Purple in person, my opinion is that OnePlus has certainly provided better color choices in the past. OnePlus today announced that it will soon be selling its OnePlus 6T flagship handset in a bold new color called Thunder Purple .
Fallout 76 has a massive day one patch
Fallout 76 pre-order customers are counting down to the release of Bethesda's next major release. Fallout 76 appears to have gone live for some players ahead of its intended release date.
Brexit Deal Agreed On "Technical Level" As PM Calls Crunch Cabinet Meeting
Britons will not need visas for short stays in the EU even if there is no Brexit deal, the European Commission has said. Downing Street believes that significant progress has been made over the past 48 hours towards meeting that deadline.
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.