Two reporters and two editors from Breitbart News have resigned in protest at how the conservative website handled an alleged assault last week on one of the reporters by a senior aide to Republican presidential candidate Donald Trump.

Reporter Michelle Fields filed a criminal complaint on Friday against Trump campaign manager Corey Lewandowski, saying he grabbed her arm at a rally on March 8 in Florida with such force that he left bruises. Lewandowski and Trump have denied the accusation.

The incident generated a spat at Breitbart, with journalists accusing management of kowtowing to the Trump campaign.

Breitbart published an account on Friday of the incident that raised questions over Fields' version of events and suggested it was not Lewandowski who grabbed her. According to a BuzzFeed report on Saturday, Breitbart senior editor-at-large Joel Pollak also ordered staffers in an internal chatroom to stop defending Fields.

Fields and editor-at-large Ben Shapiro resigned in response to that late on Sunday. National security correspondent Jordan Schachtel and editor Jarrett Stepman resigned on Monday, according to a letter by them that was posted to Twitter, in which they accused the news site of becoming a propaganda arm for the Trump campaign. 

Breitbart News Chief Executive Larry Solov did not respond to a request for comment on Monday.

The alleged assault on Fields took place days before a series of clashes between supporters of Trump, front-runner to be the Republican presidential nominee in November's election, and protesters at campaign rallies.

The allegations were being investigated, a spokesman for the Jupiter, Florida police department said on Monday. No charges have been filed, he said.