Personnel at U.S. Central Command have deleted files and emails amid allegations that intelligence assessments were altered to exaggerate progress against Islamic State militants, the chairman of the House Intelligence Committee said Thursday.   

"We have been made aware that both files and emails have been deleted by personnel at CENTCOM and we expect that the Department of Defense will provide these and all other relevant documents to the committee," Rep. Devin Nunes said at a hearing on worldwide threats facing the United States. Central Command oversees U.S. military activities in the Middle East.   

Nunes, R-Calif., also said the Office of the Director of National Intelligence briefed the committee on a survey indicating that more than 40 percent of Central Command analysts believe there are problems with the integrity of the intelligence analyses and process.   With turmoil across the Mideast, Nunes wondered aloud if it was appropriate to wait months for the Defense Department's inspector general to complete an investigation into the allegations before efforts are made to rectify the alleged problems.   

"To me, it seems like 40 percent of analysts who are concerned at CENTCOM -- that's just something that can't be ignored," Nunes said.   

A senior intelligence official said that each year the DNI conducts a survey at all 17 U.S. intelligence agencies to gain feedback on the integrity, standards and objectivity of the process used to analyze intelligence. In the most recent survey, conducted between August and October 2015, more than 100 employees from CENTCOM responded to the survey. The official spoke on condition of anonymity to disclose details of the internal survey.   

A report on the survey issued in December 2015 indicated that 40 percent of those who responded at CENTCOM answered "yes" to the question: "During the past year, do you believe that anyone attempted to distort or suppress analysis on which you were working in the face of persuasive evidence?"   

Asked whether he considered 40 percent an unusually high number, Lt. Gen. Vincent Stewart, director of the Defense Intelligence Agency, told the committee that he did.   Stewart said that while it would be favorable for all to "get closure on exactly the extent of this allegation," he cannot control the pace of the watchdog's investigation. He said that while the investigation proceeds, intelligence officials continue to look into ways to improve the process of producing the assessments, and he noted that the DIA's ombudsman had looked into a particular incident.   

The New York Times, which first disclosed the investigation, reported that the probe began after at least one civilian DIA analyst told authorities he had evidence that CENTCOM officials were improperly reworking conclusions of assessments prepared for President Barack Obama and other top policymakers.