The Pentagon launched a fresh probe Monday into a 2019 airstrike that killed civilians in Syria, two weeks after a New York Times investigation claimed the US military concealed dozens of non-combatants' deaths.

Defense Secretary Lloyd Austin instructed Army General Michael Garrett to "review the reports of the investigation already conducted into that incident" and "conduct further inquiry into the facts and circumstances related to it," Pentagon spokesman John Kirby said.

Garrett's three-month review will assess "civilian casualties that resulted from the incident, compliance with the law of war, record keeping and reporting procedures," Kirby added.

It will also probe whether measures taken after the earlier investigation were effectively implemented, if "accountability measures" should be taken and if "procedures or processes should be altered."

According to a Times investigation published mid-November, a US special force operating in Syria -- sometimes in complete secrecy -- bombed a group of civilians three times on March 18, 2019, near the Islamic State (IS) bastion of Baghouz, killing 70 people, mainly women and children.

The Times report says a US legal officer "flagged the strike as a possible war crime" but that "at nearly every step, the military made moves that concealed the catastrophic strike."

The Times found the strike "was one of the largest civilian casualty incidents of the war against the Islamic State," but was never publicly acknowledged by the US military.

"The death toll was downplayed. Reports were delayed, sanitized and classified. United States-led coalition forces bulldozed the blast site. And top leaders were not notified," the report said, adding findings of a Pentagon probe were "stalled and stripped of any mention of the strike."

A statement released by the Pentagon after the report said the initial investigation into the incident by the US Army Central Command, which oversees military operations in the Middle East, found the strikes were "self-defense," "proportional" and that "appropriate steps were taken to exclude the presence of civilians."

A US-led coalition and Kurdish-led allies announced the defeat of the IS proto-state, known as the "caliphate," at the end of March 2019 after overcoming the last jihadist holdout of Baghouz.