The Defense Department's inspector general is investigating whether intelligence reports about the progress of the U.S.-led coalition's campaign against ISIS in Iraq have been "skewed" to be more optimistic.

The New York Times first reported that at least one civilian employee of the Defense Intelligence Agency (DIA) told authorities that officials at U.S. Central Command (CENTCOM) were improperly reworking intelligence assessments prepared for policymakers, including President Obama. 

A senior military official confirmed to Fox News that an IG investigation has been initiated into the allegation. 

The Times report did not say when the assessments were allegedly altered, nor did it say who may have been responsible. Officials told the paper the investigation was focused on whether military officials had changed the conclusions of draft intelligence reports during a review before passing them on.

Under federal law, intelligence officials can bring claims of wrongdoing to the intelligence community's inspector general. U.S. officials told the paper that the House and Senate Intelligence Committees were advised of the claims within the past several weeks, as is required if officials find the claims credible. At that point, The Times reports, the Pentagon's inspector general decided to look into the matter.

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Government rules state that intelligence assessments "must not be distorted" by agendas or policy views. However, The Times reports that legitimate differences of opinion are both common and encouraged among national security officials. 

Central Command spokesman Col. Patrick S. Ryder said in a statement Wednesday that they welcome the IG's "independent oversight." 

"While we cannot comment on ongoing investigations, we can speak to the process and about the valued contributions of the Intelligence Community (IC)," he said, adding that intelligence community members typically are able to comment on draft security assessments. "However," he said, "it is ultimately up to the primary agency or organization whether or not they incorporate any recommended changes or additions. Further, the multi-source nature of our assessment process purposely guards against any single report or opinion unduly influencing leaders and decision-makers." 

The DIA is one of many intelligence agencies that has produced assessments about the progress of the Iraq campaign. According to The Times, analysts from one agency may make suggestions about another agency's draft analyses, but it is up to the authoring agency to decide whether to adopt those suggestions. 

The U.S. began launching airstrikes against ISIS in Iraq in August 2014, and did the same in Syria the following month. Last month, however, U.S. intelligence concluded that the terror group was not fundamentally weaker than it was when the aerial campaign began. Officials said that while intervention by the U.S.-led coalition had prevented the collapse of the Iraqi government and resulted in the rollback of some gains made by ISIS in the summer of 2014, the extremist group remained a well-funded army able to replenish its ranks with foreign jihadis as quickly as the U.S. can eliminate them. The intelligence assessment also found that ISIS had expanded to other countries, including Libya, Egypt and Afghanistan.

However, earlier that month, retired Army Gen. John Allen, the White House's top envoy to other nations in the anti-ISIS coalition, told an audience at the Aspen Security Forum  that ISIS had been "checked strategically, operationally, and by and large, tactically," adding, more bluntly, "ISIS is losing."

Click for more from The New York Times. 

Fox News' Lucas Tomlinson contributed to this report.