Attorney General Jeff Sessions designated U.S. attorney John Huber as the prosecutor tasked with looking into allegations of abuse of power at the FBI.

In a Thursday letter to Congress, Sessions said this appointment was made in response to requests for a special counsel investigation of the claims. The attorney general said, however, that Huber will be the one determining "whether any matters merit the appointment of a special counsel."

Sessions cited Justice Department regulations which stipulate that a special counsel appointment should be reserved for only the most "extraordinary circumstances."

If the situation doesn't "justify such a departure 'from the normal processes of the Department,'" Sessions said the guidelines allow the attorney general to make alternative arrangements that would sufficiently "mitigate any conflicts of interest."

Huber will conduct his investigation from outside Washington, D.C. and in cooperation with Inspector General Michael Horowitz, Sessions said.

Trump and several Republicans allies in Congress have accused the FBI and the Justice Department of political bias.

In February, President Donald Trump agreed to let Republicans on the House Intelligence Committee release a memo alleging surveillance abuses at the FBI and Justice Department. The FBI and Justice Department, in turn, objected to the release.

The memo alleged anti-Trump bias at the FBI, but Democrats and other observers criticized the memo for being unbalanced and leaving too many points out. The Democrats' rival memo, which sought to contradict many of the GOP points, was also eventually released, but it was riddled with redactions recommended by the Justice Department.

In his letter, Sessions said he will take the necessary actions to defend the integrity of the Justice Department and its work.

"We understand that the Department is not above criticism and it can never be that the Department conceals errors when they occur," Sessions wrote.

The attorney general said he expects the department's staff to operate with the "highest level of integrity, ethic, and professionalism."

"If anyone falls short of these standards, I will fulfill my responsibility to take necessary action to protect the integrity of our work," he said.

This is breaking news. Please check back for updates.

— CNBC's Kevin Breuninger contributed to this report.