A US review of the 2021 Kabul airport bombing has uncovered classified documents that should have been previously disclosed, according to Sean Parnell, chairman of the Afghanistan Withdrawal Special Review Panel and a senior adviser to War Secretary Pete Hegseth.

Parnell announced the discovery Wednesday in remarks marking the fifth anniversary of the Aug. 26, 2021, bombing at Abbey Gate outside Kabul airport, which killed 13 US service members and about 170 Afghans during the US-led evacuation.

"Recently, my team recovered highly relevant classified documents - material that should have been disclosed - stashed and hidden away in safes where they would not be found," Parnell said.

Parnell said that after the documents were examined by the special review panel, "it became clear why someone tried to hide them." He did not identify who he believed had concealed the documents or disclose their contents, saying the material remains classified.

"I`m not going to give you a convenient version of the truth, nor will I give you a rushed one," Parnell said. "We are following the evidence to wherever it leads and to whoever it touches."

Hegseth appointed Parnell, an Afghanistan war veteran, to lead the Afghanistan Withdrawal Special Review Panel. The panel is examining the circumstances surrounding the US withdrawal from Afghanistan and the Abbey Gate bombing.

Parnell said members of the panel have extensive military experience in Afghanistan.

"These patriots commanded troops; they took fire; they carried the wounded, and they buried their friends," he said. "They knew how decisions in Afghanistan became consequences because they are the ones who lived with them."

The panel`s work follows a supplemental review by US Central Command in April 2024 that revisited the military`s original investigation into the Abbey Gate attack. That review upheld the earlier finding that the bombing could not have been prevented at the tactical level.

ISIS-K claimed responsibility for the attack, which occurred as thousands of Afghans gathered outside Kabul airport seeking evacuation following the Taliban takeover.

Parnell did not provide a timeline for completing the latest review but said the panel would continue following the evidence and examining decisions surrounding the withdrawal.

"The American people and the families who sacrificed everything are owed the full picture of how and why those decisions were made, and we`re going to give it to them," Parnell said.