WASHINGTON (Reuters) -U.S. President Joe Biden's son Hunter Biden on Wednesday asked a federal court's permission to subpoena documents from former President Donald Trump and senior Justice Department officials in his administration as part of his defense against federal gun charges.

The younger Biden's lawyers cited public reporting suggesting "incessant, improper, and partisan pressure" applied by Trump to former Attorney General William Barr and senior Justice Department officials Richard Donoghue and Jeffrey Rosen to investigate Biden.

Hunter Biden, 53, in October pleaded not guilty to charges that he lied about his drug use while buying a handgun, in the first-ever criminal prosecution of a sitting U.S. president's child.

(Reporting by Andrew Goudsward; Editing by Scott Malone)