The 22-year sentence for a Libyan militant convicted of four terrorism charges for his involvement in the 2012 Benghazi attack is "unreasonably low," a federal appeals court ruled Tuesday. 

Ahmed Abu Khatallah, 51, was convicted of four counts in 2017, including providing material support to terrorists and destroying US property, but was acquitted on the most serious charges. 

Four Americans were killed in the attack on a US diplomatic compound and a CIA complex in Benghazi, Libya, on Sept. 11, 2012. 

Sentencing guidelines said that Khatallah should have been sentenced to 30 years to life in prison, according to prosecutors. 

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The US Court of Appeals for the DC Circuit ruled Tuesday that 22 years in prison is not long enough for Khatallah "given the gravity of such an assault on an American diplomatic facility and the district court’s own recognition of the vital need to deter such crimes." 

"In sentencing Khatallah to just twelve years for the two support-of-terrorism counts and the property destruction count, the district court did not—and could not on this record—sufficiently justify its additional variance so far below the sentencing range that would have been appropriate even without any consideration of acquitted conduct," the three-judge panel wrote. 

Khatallah motioned for a mistrial both before and after the verdict, then appealed his sentence in 2020, but prosecutors cross-appealed. 

The appeals court remanded Khatallah for resentencing. 

The Associated Press contributed to this report.