WASHINGTON - Eighteen years after the September 11, 2001, terror attacks pushed the United States and its allies to launch the war on terrorism, veteran counterterrorism officials warn the coalition is helping history repeat itself.

A group of 13 former officials, including two former directors of the U.S. National Counterterrorism Center, the former director of counterterror operations at Britain's MI6 and the former U.S. envoy to the coalition targeting the Islamic State terror group, issued an open letter late Tuesday urging Western countries to stop ignoring detainees in Syria and Iraq.

"We have borne witness to the violent rise of al-Qaida, the Taliban, and ISIS," they wrote, using an acronym for Islamic State.

"We have studied the conditions that brought those groups into being and allowed them to grow in strength," they said. "We see some of the same conditions arising once again."

In particular, the officials focus on the al-Hol camp in northeastern Syria, home to an estimated 70,000 people displaced during the U.S.-led fight to destroy IS' self-declared caliphate.

According to data compiled by Human Rights Watch, about 11,000 are thought to be women and children related to suspected IS fighters.

Despite repeated requests by U.S. officials, many European countries have been reluctant to take many of them back.

The former counterterrorism and national security officials call that a mistake.

"This 'hands-off' stance will only create greater danger in the future," the officials wrote. "The denial of citizenship by their home nations will bolster their sense of being, in effect, citizens of the Islamic State, potentially preparing them to form the core of a future resurgence."

Speaking at a panel in Washington Tuesday, Brett McGurk, former U.S. envoy to the Defeat IS coalition, called the situation with the detainees unsustainable.

"We've got to have some focused priorities, and al-Hol is really critical," McGurk told an audience at the Washington-based Brookings Institution, calling the camp and the prison facilities holding about 2,000 foreign fighters "Jihad-land."

"We know what happens in these prisons," he said, noting such centers had served as incubators for al-Qaida in Iraq leader Abu Musab al Zarqawi, as well as IS leader Abu Bakr al-Baghdadi.

"I hope the U.S. steps up to this because it's very serious," McGurk said. "It's central to our national security interests."

"After 18 years of this so-called war on terrorism, we spend more than, I don't know, it's reported $5 to $6 trillion," Ali Soufan, a former FBI supervisory special agent and a signatory of the letter, told U.S. lawmakers Tuesday. "And now we have more terrorists than when we started on 9/11. What we're doing internationally, globally, is not working."