Washington (CNN) The Justice Department's internal watchdog announced Wednesday it has launched a probe into the department and the FBI's handling of warrant applications under the Foreign Intelligence Surveillance Act.

The review by Inspector General Michael Horowitz came after requests from Attorney General Jeff Sessions and members of Congress, the IG's office said.

For weeks, President Donald Trump and his allies on Capitol Hill have pointed to the House Intelligence Committee's controversial memo -- the so-called Nunes Memo -- slamming how the FBI obtained a FISA warrant to monitor Trump foreign policy aide Carter Page to argue that the nation's top law enforcement agency is politically biased. The memo claims the FBI failed to adequately inform the judge who approved the warrant that it relied, in part, on opposition research funded by the Democratic National Committee and Clinton's campaign.

The IG "will review information that was known to the DOJ and the FBI at the time the applications were filed from or about an alleged FBI confidential source," Horowitz's office said. The investigation will also "review the DOJ's and FBI's relationship and communications with the alleged source as they relate to the (Foreign Intelligence Surveillance Court) applications."

Sessions told reporters last month that Horowitz's office was looking at whether the FBI handled the FISA warrant on Page properly -- prompting Trump to lash out on Twitter and causing Sessions to respond with a rare statement defending his "integrity and honor."

Read More