White House chief of staff John Kelly and White House national security adviser John Bolton hurled expletives at one another during a loud argument outside the Oval Office on Thursday.

The exchange between the two was so heated, White House aides were concerned that either Kelly or Bolton would depart their posts immediately, Bloomberg reports.

Sources said the dispute began over a disagreement on how to handle the surge in border crossings, and Bolton was critical of how Homeland Security Secretary Kirstjen Nielsen was handling her job. President Trump, who earlier in the day threatened to “close our southern border” as a Honduran caravan approaches, picked Bolton's side on the matter.

Neither Bolton nor Kelly are planning on resigning, according to three sources familiar with the situation.

Although sources said Trump witnessed the beginning of the contentious exchange, he later claimed he had no knowledge of it.

"I've not heard about it. No," Trump told reporters Thursday afternoon when asked about the fight, per CNN.

The White House did not immediately respond to a request for comment from the Washington Examiner.

Kelly joined the White House last summer, replacing outgoing White House chief of staff Reince Preibus. He previously served as the head of the Department of Homeland Security, and pushed for Nielsen succeed him.

Bolton has been serving in the White House since April, succeeding H.R. McMaster as the White House’s national security adviser.