Washington (AP): Kash Patel was sworn in as the FBI director and he called the opportunity to lead the nation's premier federal law enforcement agency the "greatest honour" of his life.

Patel was confirmed by the Senate on Thursday by a 51-49 margin, with two Republican lawmakers, Susan Collins of Maine and Lisa Murkowski of Alaska, breaking party ranks and voting against him.

"I think he'll go down as the best ever at that position," President Donald Trump told reporters Friday ahead of the White House swearing-in on Friday, which was conducted by Attorney General Pam Bondi and attended by Republican supporters in Congress, including Sen. Ted Cruz of Texas and Rep. Jim Jordan of Ohio.

Trump added that the "agents love this guy".

Patel will inherit an FBI gripped by turmoil as the Justice Department over the past month has forced out a group of senior bureau officials and made a highly unusual demand for the names of thousands of agents who participated in investigations related to the January 6, 2021, riot at the US Capitol.

Democrats had sounded the alarm about the appointment, saying they fear Patel will operate as a loyalist for Trump and abuse the FBI's law enforcement powers to go after the president's adversaries. They've cited past comments such as his suggestion before he was nominated that he would "come after" anti-Trump "conspirators" in the government and media.

Patel sought to assuage those concerns at his confirmation hearing last month, saying he intended to follow the Constitution and had no interest in pursuing retribution, though he also said at his swearing-in Friday that reporters had written "fake, malicious, slanderous and defamatory" stories about him.

Republicans angry over what they see as law enforcement bias against conservatives during the Democratic Biden administration, as well as criminal investigations into Trump, have rallied behind Patel as the right person for the job.

Patel has spoken of his desire to implement major changes at the FBI, including a reduced footprint in Washington and a renewed emphasis on the bureau's traditional crime-fighting duties rather than the intelligence-gathering work that has come to define its mandate over the past two decades as national security threats have proliferated.

He said Friday that the FBI's "national security mission" was equally as important as its efforts to fight violent crime and drug overdoses.

"Anyone that wishes to do harm to our way of life and our citizens, here and abroad, will face the full wrath of the DOJ and FBI," Patel said. "If you seek to hide in any corner of this country or planet, we will put on the world's largest manhunt and we will find you and we will decide your end-state."

A former Justice Department counterterrorism prosecutor, Patel was selected in November to replace Christopher Wray, who was picked by Trump in 2017 and who resigned at the conclusion of the Biden administration to make way for his chosen successor.

Wray infuriated Trump throughout his tenure, including after FBI agents searched his Mar-a-Lago estate in Florida in August 2022 for classified documents in one of two federal investigations that resulted in indictments against Trump that were dismissed after his election win.

FBI directors are given 10-year terms as a way to insulate them from political influence and keep them from becoming beholden to a particular president or administration. But Trump fired the FBI director he inherited, James Comey, after Comey had spent over three years on the job and replaced Wray after more than seven years in the position.