A suspect linked to the alleged assassination attempt on U.S. President Donald Trump during the White House correspondents’ dinner in Washington, D.C., has pleaded not guilty to four federal charges. 

The suspect, identified as 31-year-old Cole Tomas Allen from California, appeared before a federal court in Washington on Monday, where his attorney entered the plea on his behalf. 

Mr Allen has been charged with attempted assassination of the president, assault on a federal officer, transporting firearms to commit a felony and discharging a firearm during a violent crime. 

Prosecutors alleged that he attempted to breach security at the Washington Hilton during the annual press gala attended by Mr Trump, senior officials and journalists. 

According to investigators, he fired a shotgun at a Secret Service agent while trying to force his way through a security checkpoint. 

The agent survived after being protected by a ballistic vest before Mr Allen was subdued and arrested at the scene. 

Federal authorities also claimed the suspect travelled from California to Washington days before the event and was carrying multiple weapons, including a shotgun, a pistol and knives. 

During the hearing, the suspect wore an orange jumpsuit and remained cuffed as proceedings lasted briefly before U.S. District Judge Trevor McFadden. 

His attorneys argued that Justice Department lawyers Todd Blanche and Jeanine Pirro should step away from the prosecution because both attended the gala and could be considered connected to the incident. 

The suspect remains in federal custody pending further hearings as investigations into the motive behind the attempted attack continue. 

The next hearing is scheduled for June 29, at which both the prosecution and the defence are expected to present additional pre-trial motions and evidence.