With the Taliban growing more violent and adding checkpoints near Kabul's airport, an all-volunteer group of American veterans of the Afghan war launched a final daring mission on Wednesday night dubbed the "Pineapple Express" to shepherd hundreds of at-risk Afghan elite forces and their families to safety, members of the group told ABC News.

Moving after nightfall in near-pitch black darkness and extremely dangerous conditions, the group said it worked unofficially in tandem with the United States military and U.S. embassy to move people, sometimes one person at a time, or in pairs, but rarely more than a small bunch, inside the wire of the U.S. military-controlled side of Hamid Karzai International Airport.

The Pineapple Express' mission was underway Thursday when the attack occurred in Kabul. There were wounded among the Pineapple Express travelers from the blast, and members of the group said they were assessing whether unaccounted-for Afghans they were helping had been killed.

As of Thursday morning, the group said it had brought as many as 500 Afghan special operators, assets and enablers and their families into the airport in Kabul overnight, handing them each over to the protective custody of the U.S. military. "Dozens of high-risk individuals, families with small children, orphans, and pregnant women, were secretly moved through the streets of Kabul throughout the night and up to just seconds before ISIS detonated a bomb into the huddled mass of Afghans seeking safety and freedom," Army Lt. Col. Scott Mann, a retired Green Beret commander who led the private rescue effort, told ABC News.

The week-long effort and Wednesday's operation were observed by ABC News under the agreement of secrecy while the heart-pounding movements unfolded.

The operation carried out Wednesday night was an element of "Task Force Pineapple," an informal group whose mission began as a frantic effort on Aug. 15 to get one former Afghan commando who had served with Mann into the Kabul airport as he was being hunted by the Taliban who were texting him death threats. They knew he had worked with U.S. Special Forces and the elite SEAL Team Six for a dozen years, targeting Taliban leadership, and was, therefore, a high-value target for them, sources told ABC News.

"This Herculean effort couldn't have been done without the unofficial heroes inside the airfield who defied their orders to not help beyond the airport perimeter, by wading into sewage canals and pulling in these targeted people who were flashing pineapples on their phones," Mann said.

Looking back at an effort that saved at least, by their count, 630 Afghan lives, Jason Redman, a combat-wounded former Navy SEAL and author, who was shepherding Afghans he knew,  expressed deep frustration "that our own government didn't do this. We did what we should do, as Americans."