The Pentagon’s inspector general is investigating allegations that military officials have skewed intelligence assessments about the United States-led campaign in Iraq against the Islamic State to provide a more optimistic account of progress, according to several officials familiar with the inquiry.

The investigation began after at least one civilian Defense Intelligence Agency analyst told the authorities that he had evidence that officials at United States Central Command — the military headquarters overseeing the American bombing campaign and other efforts against the Islamic State — were improperly reworking the conclusions of intelligence assessments prepared for policy makers, including President Obama, the government officials said.

Fuller details of the claims were not clear, including when the assessments were said to have been altered and who at Central Command, or Centcom, the analyst said was responsible. The officials, speaking only on condition of anonymity about classified matters, said that the recently opened investigation focused on whether military officials had changed the conclusions of draft intelligence assessments during a review process and then passed them on.