A midlevel member of the Trump State Dept. has been arrested on charges related

The F.B.I. said on Thursday that it had arrested a former State Department aide on charges related to the Jan. 6 attack on the Capitol, including unlawful entry, violent and disorderly conduct, obstructing Congress and law enforcement, and assaulting an officer with a dangerous weapon.

The former midlevel aide, Federico G. Klein, who federal investigators said in court documents was seen in videos of the riot resisting officers and assaulting them with a stolen riot shield, is the first member of the Trump administration to face criminal charges in connection with the storming of the Capitol by a pro-Trump mob.

He worked on Donald J. Trump’s 2016 presidential campaign and began working at the State Department just days after Mr. Trump’s inauguration in January 2017, according to a financial disclosure form he filed as an executive branch employee.

Mr. Klein’s arrest was reported earlier by Politico.

The F.B.I. said in a court document that it received a tip about Mr. Klein in January, on the day after it included his image in a poster seeking information about several people seen in the crowd that had stormed the Capitol. A tipster provided investigators with Mr. Klein’s Facebook account, and a different witness later contacted them to say that he knew the man in the poster as “Freddie Klein,” according to the document.

Based on this information, the F.B.I. determined that when Mr. Klein allegedly attacked Congress on Jan. 6 to help Mr. Trump unlawfully maintain power, he was still employed by the State Department and possessed a Top Secret security clearance, the bureau said in the document.

Mr. Klein can be seen in video footage and other images dressed in a red “Make America Great Again” hat, slacks and a dress shirt as he tries to break past a line of Metropolitan Police officers in a tunnel near the west terrace, according to the document. “Klein quickly pushed his way to the front-left side of the crowd and to the doorway to the Capitol building, where he physically and verbally engaged with the officers holding the line,” the F.B.I. said.

He was part of a mob that tried to push through the doors despite warnings by an officer to back up, the F.B.I. said, and used a “riot shield that apparently had been taken from an officer” to prevent the closing of the doors.

Mr. Klein was seen in other videos “calling back to the crowd behind him, ‘We need fresh people, we need fresh people’ multiple times,” the F.B.I. said.

The Justice Department’s aggressive and sprawling investigation into the attack on the Capitol has led to criminal charges against more than 300 people, including dozens of far-right extremists who have been accused of conspiring to attack Congress in order to stop the final certification of Joseph R. Biden Jr.’s Electoral College victory.

Many defendants have said that they acted at the behest of Mr. Trump, who had falsely asserted that he won the November election.

In recent weeks, the investigation has edged closer to Mr. Trump. Last month, investigators began examining the communications of some right-wing extremists who had breached the Capitol to determine whether Roger J. Stone Jr., a close…