FBI Director Christopher Wray has launched a staunch defence of the agency following criticism by US President Donald Trump.
Mr Wray told a committee of lawmakers that there was “no finer institution”.
Mr Trump recently lashed out at the federal law enforcement agency, saying its reputation was “in tatters”.
Special Counsel Robert Mueller, a former FBI director, is investigating alleged Russian interference in the US election.
Mr Trump denies that his team colluded with Moscow to get him elected.
“The FBI that I see is tens of thousands of brave men and women working as hard as they can to keep people they will never know safe from harm,” Mr Wray told the House Judiciary Committee, according to the Associated Press.
He described the bureau’s staff as “decent people committed to the highest principles of integrity and professionalism”.
Reports emerged last weekend that Mr Mueller had dismissed an FBI officer from the investigation after he was discovered to have made anti-Trump remarks in text messages.
The president seized on the officer’s dismissal, and in a tirade on Twitter he said the FBI’s “reputation is in Tatters – worst in history! But fear not, we will bring it back to greatness”.
President Trump also issued a fresh denial that he asked former FBI director James Comey to drop an investigation into the conduct of one of his top aides, Michael Flynn.