Nearly 500 civilians were killed in U.S. military operations in President Donald Trump's first year in office, a Pentagon report to Congress estimates.

"The Department of Defense (DoD) assesses that there are credible reports of approximately 499 civilians killed and approximately 169 civilians injured during 2017," the report said, noting military operations against Daesh terror group in Iraq, Syria, Afghanistan and Yemen, and against Taliban in Afghanistan and al-Qaeda in Yemen.

The counter-terrorism report said the DoD had "no credible reports" of civilian casualties due to U.S. military actions in Libya or Somalia in 2017.

However, "more than 450 reports of civilian casualties from 2017 remained to be assessed," the report added, indicating the casualty count could increase.

The report includes civilian casualties in both ground combat operations and airstrikes.

Airstrikes in Syria, Iraq, Afghanistan, Yemen and Somalia increased significantly during the Trump administration's first year. In Afghanistan, the number of strikes jumped nearly quarterfold, to 4,361 in 2017 from 1,337 in 2016. The number of strikes in Syria and Iraq climbed to 39,577 from 30,743 in the same period, according to the Air Forces Central Command.

"Despite the best efforts of U.S. forces, civilian casualties are a tragic but at times unavoidable consequence of combat operations," the Pentagon said, attributing the casualties to the use of human shields and other endangering tactics by Daesh and al-Qaeda in urban areas.

The report was delivered under a mandate signed into effect by executive order by then-President Barack Obama in 2016.

The order mandated "an annual summary" including terrorist and civilian casualties as well as "the number of strikes undertaken by the U.S. Government against terrorist targets" in areas outside active conflict sites.

Though Obama's order specified the report would be made public "annually on May 1," the Trump administration missed the deadline, drawing criticism from human rights groups.

On Thursday, the U.S.-led coalition combating Daesh in Iraq and Syria reported "at least 892 civilians have been unintentionally killed" in 29,358 coalition strikes from August 2014 through the end of April 2018.

However, outside groups put the number of civilians killed much higher than the coalition's count.

While the DoD acknowledged the discrepancies, it attributed them to "different types of information and different methodologies to assess whether civilian casualties have occurred."