Active-service members and veterans provided first-hand testimony Wednesday about the chaotic American withdrawal from Afghanistan, describing in harrowing detail the carnage and death they witnessed on the ground while imploring Congress to help the allies left behind.

A former Marine sergeant, Tyler Vargas-Andrews, testified to Congress about the stench of human flesh under a large plume of smoke as the screams of children, women, and men filled the space around Kabul’s airport after two suicide bombers attacked crowds of Afghans.

“The withdrawal was a catastrophe in my opinion. And there was an inexcusable lack of accountability and negligence,” Sergeant Vargas-Andrews, who wore a prosthetic arm and scars of his own grave wounds from the bombing, said.

“I see the faces of all of those we could not save, those we left behind,” an Army medic who was stationed at Abbey Gate, Aidan Gunderson, testified. “I wonder if our Afghan allies fled to safety or they were killed by the Taliban.”

The initial hearing of a long-promised investigation by House Republicans displayed the open wounds from the end of America’s longest war in August 2021, with witnesses recalling how they saw mothers carrying dead babies and the Taliban shooting and brutally beating people.

It was the first of what is expected to be a series of Republican-led hearings examining what is widely perceived as the Biden administration’s rushed and feckless handling of the withdrawal. Taliban forces seized the Afghan capital, Kabul, far more rapidly than American intelligence services had foreseen as American forces pulled out. Kabul’s fall turned the West’s withdrawal into a rout, with Kabul’s airport the center of a desperate air evacuation guarded by U.S. forces temporarily deployed for the task.

The majority of witnesses argued to Congress that the fall of Kabul was an American failure with blame touching every presidential administration from George W. Bush to Joe Biden. Testimony focused not on the decision to withdraw, but on what witnesses depicted as a desperate attempt to rescue American citizens and Afghan allies with little U.S. planning and inadequate U.S. support.

“America is building a nasty reputation for multi-generational systemic abandonment of our allies where we leave a smoldering human refuse from the Montagnards of Vietnam to the Kurds in Syria,” a retired lieutenant colonel, Scott Mann, testified before the House Foreign Affairs Committee.

He added, “Our veterans know something else that this committee might do well to consider: We might be done with Afghanistan, but it’s not done with us.”

Sergeant Vargas-Andrews said Marines and others aiding in the evacuation operation were given descriptions of men believed to be plotting an attack before it occurred. He said he and others spotted two men matching the descriptions and behaving suspiciously, and eventually had them in their rifle scopes, but never received a response about whether to take action.

“No one was held accountable,” Sergeant Vargas-Andrews told Representative Mike McCaul, the Republican of Texas who is the chairman of the committee. “No one was, and no one is, to this day.”

U.S. Central Command’s investigation concluded in October 2021 that given the worsening security situation at Abbey Gate as Afghans became increasingly desperate to flee, “the attack was not preventable at the tactical level without degrading the mission to maximize the number of evacuees.” However, that investigation did not look into whether the bomber could have been stopped or whether Marines on the ground had the appropriate authorization to engage.

A Defense Department spokesman, Lieutenant Colonel Rob Lodewick, said Wednesday that the Pentagon’s earlier review of the suicide attack had turned up neither any advance identification of a possible attacker nor any requests for “an escalation to existing rules of engagement” governing use of force by U.S. troops.

The witnesses testifying Wednesday urged action to help the hundreds of thousands of Afghan allies who worked alongside American soldiers and who are now in limbo in the U.S. and back in Afghanistan.

Last month, the U.S. inspector-general for Afghanistan, John Sopko, concluded again that certain actions taken by the Biden administrations contributed to the swift collapse of the Afghan government and military, even before American forces completed their withdrawal in August 2021.

Those actions included but were not limited to the  abruptness of Mr. Biden’s withdrawal of both American contractors and troops from Afghanistan and stranding an Afghan air force that previous administrations had failed to make self-supporting.

Mr. McCaul, for his part, has been deeply critical of the Biden administration’s handling of the withdrawal. The Republican lawmaker vowed to hold accountable every Biden administration official responsible for what he called the “abdication of the most basic duties of the United States government to protect Americans and leave no one behind.”

He added, “What happened in Afghanistan was a systemic breakdown of the federal government at every level, and a stunning failure of leadership by the Biden administration.”