A former Army Special Forces officer is blasting Donald Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's pick for secretary of Defense, accusing retired Marine Corps. Gen. James Mattis of "leaving my men to die" more than a decade ago.

Jason Amerine says that when a team of Special Forces was hit by friendly fire in Afghanistan in December 2001, Mattis, who was in charge of a nearby group of Marines, hesitated to approve a rescue operation.

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"Every element in Afghanistan tried to help us except the closest friendly unit, commanded by Mattis. Men were ready to drive to get us or send horses from the other side of the country if that was what it took," Amerine wrote in a Facebook post.

Sources involved in the operation told NBC News that Mattis, who was a brigadier general at the time, turned down repeated requests for assistance even though helicopters under his command were reportedly just 45 minutes away.

Mattis retired in 2013 after leading U.S. Central Command, meaning he would need a special waiver from Congress to serve atop the Pentagon, which requires former military officers be out of uniform for seven years before becoming Defense chief.

Mattis has not commented publicly on the incident, which NBC News noted was detailed in the 2011 book "The Only Thing Worth Dying For" by Eric Blehm. Neither Trump's transition team nor Mattis offered comment for the NBC report.

The former Special Forces officer wrote Friday that the long delay may have caused the deaths of several soldiers, but added that the incident was never properly investigated by officials.

"None of that was assessed properly because the [5th Special Forces Group] chose not to call for a formal investigation. 5th Group wanted to end the bad press associated with the friendly fire and the inaction by Mattis only made it worse so they buried my angry complaints and sought to shut me up about everything that happened that day," he wrote.

Amerine underscored his criticism of the former general by accusing him of being "indecisive" and "betray[ing] his duty."

"Maybe Mattis was a good general later in his career by whatever standard you want but it has been bizarre to suddenly see these facts up for debate. He was indecisive and betrayed his duty to us, leaving my men to die during the golden hour when he could have reached us," Amerine wrote.