Jeff Sessions fired back Wednesday at criticism from President Donald Trump, saying in a statement that “as long as I am the Attorney General, I will continue to discharge my duties with integrity and honor.”
Mr. Sessions’s statement came hours after Mr. Trump chastised his attorney general’s decision to refer a probe of the Justice Department’s handling of secret surveillance warrants to the agency’s inspector general rather than another office.
“Why is A.G. Jeff Sessions asking the Inspector General to investigate potentially massive FISA abuse. Will take forever, has no prosecutorial power…Why not use Justice Department lawyers? DISGRACEFUL!” Mr. Trump said.
The tweet followed a disclosure by Mr. Sessions on Tuesday that the Justice Department’s inspector general, Michael Horowitz, would investigate how the FBI and federal prosecutors obtained warrants from the nation’s secret spy court to spy on a former Trump campaign foreign-policy adviser who had previously been targeted by Russian intelligence for recruitment.
Mr. Sessions has often found himself the target of criticism by Mr. Trump, particularly on Twitter. Mr. Trump has expressed frustration that Mr. Sessions recused himself a year ago from overseeing the federal investigation into Russia’s interference in the 2016 election. That investigation is now being headed by Special Counsel Robert Mueller.

For the most part, Mr. Sessions has sought to stay focused on his job and not engage the president. But associates of Mr. Sessions say Wednesday morning’s tweet crossed a line because Mr. Trump wasn’t personally bashing the attorney general or making generic complaints about the attorney general not investigating a political rival. In Mr. Sessions’s view, the president was asking him to take concrete investigative steps and not follow standard procedure, which would be a referral to the inspector general.
“We have initiated the appropriate process that will ensure complaints against this Department will be fully and fairly acted upon if necessary,” Mr. Sessions said in his statement. “As long as I am the Attorney General, I will continue to discharge my duties with integrity and honor, and this Department will continue to do its work in a fair and impartial manner according to the law and Constitution.”
Allegations of wrongdoing by Justice Department personnel are generally first referred to the inspector general for review, because that office reports both to Congress and to the department, giving it a degree of independence that the rest of the agency doesn’t have, said Michael Bromwich, who served as the Justice Department’s inspector general in the 1990s.
“There is no question in my mind that the appropriate entity to investigate will be the IG,” said Mr. Bromwich.
In a memo released this month, House Republicans said Justice Department and Federal Bureau of Investigation officials had improperly obtained a warrant from the Foreign Intelligence Surveillance Court to spy on Carter Page, a onetime Trump campaign adviser.

The memo by Republicans on the House Intelligence Committee alleged that top law-enforcement officials sought to use information paid for by the Democratic Party in 2016 to monitor Mr. Page without adequately disclosing the partisan nature of the information. Those allegations and others suggested partisan motives were behind the investigation of possible ties between the president’s associates and Russia.
The White House has denied any collusion between Russia and the Trump campaign took place, and Mr. Page hasn’t been accused of wrongdoing. Moscow has denied meddling in the U.S. election.
Democrats on the committee on Saturday released their own memo stating law-enforcement officials had indeed disclosed the political origins of the information. Their memo rejected any contention that law enforcement agents had partisan motives.
“We believe the Department of Justice must adhere to the highest standards in the [FISA] court, and yes it will be investigated, and I think that’s just the appropriate thing,” Mr. Sessions said Tuesday. “The inspector general will take that as one of the matters he’ll deal with.”
A spokesman for the inspector general’s office, John Lavinsky, confirmed Mr. Sessions requested a review of the FISA allegations but declined to comment further.
Jamil Jaffer, who worked in the George W. Bush White House and in the Justice Department’s national security division, said the inspector general’s office was the right place for any investigation into any alleged improprieties in the surveillance process.
In his Wednesday tweet, Mr. Trump also criticized Mr. Horowitz, the Justice Department inspector general, saying he was “already late with reports on Comey etc.” adding “Isn’t the I.G. an Obama guy?”
Mr. Horowitz was appointed to the post by former President Barack Obama in 2011. He was a lawyer in private practice at the time, and had previously worked as a federal prosecutor for 11 years, including as chief of the public corruption unit in the U.S. attorney’s office in Manhattan. He was also appointed by President Bush to the U.S. Sentencing Commission, where he served for five years.

The Justice Department’s inspector general post is nominated by the president and confirmed by the Senate, but doesn’t serve a specific term, to give the office a degree of independence.
In January 2017, Mr. Horowitz’s office announced it would review the Justice Department and FBI’s public actions around the investigation into Hillary Clinton’s email server. Mr. Horowitz said in November he expects the report to be complete in March or April 2018, a timeline that isn’t unusual for major investigations.
The inspector general’s office generally issues a public statement when it opens a full investigation, similar to the January 2017 statement about the Clinton review. It has issued no comparable statement yet about the Page FISA matter.
Mr. Trump’s Wednesday tweet is the latest in a series of criticisms he has leveled at the Justice Department and the FBI in general, and Mr. Sessions in particular.
Last Thursday, Mr. Sessions joined the president at the White House for a school safety round table with local leaders.
Mr. Trump began the meeting by saying, “I also want to thank a really tremendous attorney general.” He turned to the person seated next to him and added: “That’s Pam Bondi, from Florida.” Ms. Bondi is Florida’s state attorney general.
—Julie Bykowicz contributed to this article.