The determination came out at the same time that President Barack Obama was chairing a U.N. summit on countering violent extremism, in which he stressed America's successes in combating ISIS even as he acknowledged that more needed to be done on this "very difficult challenge."
More than 25,000 foreigners have flocked to war-torn Syria and Iraq since 2011 to fight with Islamist terrorist groups including ISIS, according to U.S. government estimates noted in the report.
"Despite concerted efforts to stem the flow, we have largely failed to stop Americans from traveling overseas to join jihadists," the task force determined in its report.
In just the last nine months, more than 7,000 foreign fighters have swelled the ranks of those radical militant groups waging war and committing atrocities in Iraq and Syria. And while most recruits continue to come from the Middle East and North Africa, thousands of Westerners have traveled to fight in the region -- including more than 250 Americans, more than half of which have left in the last year.
Those figures prompted the eight-member task force, commissioned by the House Homeland Security Committee and including three House Democrats, to call for an overhaul of the U.S. strategy to stem the flow and threat of foreign fighters in what the task force called "the largest global convergence of jihadists in history."
"We have to have a strategy to deal with this: both a military strategy abroad, a political solution, but also a prevention strategy here in the United States to prevent this threat," Homeland Security Committee Chairman Michael McCaul, a Texas Republican, said at a press conference announcing the reports conclusions Tuesday.
Meanwhile, at the U.N. summit on how to counter ISIS and the threat of extremism worldwide, Obama touted the work of the U.S.-led coalition in making gains against ISIS as well as the work of countries to strengthen laws "to disrupt the flow of foreign terrorist fighters."
"We share more information and we are strengthening border controls. We've prevented would-be fighters from reaching the battlefields and returning to threaten our countries. But this remains a very difficult challenge and today we are going to focus how we can do more together," Obama said Tuesday.
And while Russia and Iran did not attend the forum, Obama reiterated at the meeting that "we are prepared to work with all countries, including Russia and Iran, to find a political mechanism" to transition Syrian President Bashar al-Assad out of power.
Federal officials, for their part, have ramped up their efforts to stop and arrest individuals inspired by ISIS to either travel to Syria and Iraq or carry out attacks on U.S. soil, but gaps still remain. Of the more than 250 American who sought to travel to Iraq and Syria, U.S. officials caught just 28 before they could make it to the region, according to the task force's report.
The task force also estimated that women account for more than 30 of the 250-plus Americans who have traveled to join extremist groups in Iraq and Syria.
Texas Republican Rep. Will Hurd, who worked for nine years as an undercover CIA agent, said that while coordination between agencies fighting to prevent attacks on U.S. soil still needs work, he said he's noticed improvements.
"One of the good things is information sharing has improved since I joined the CIA back in 2000, but there's still a lot more work to be done," Hurd said Tuesday.
The group also pointed to gaps in international intelligence sharing efforts, noting that "there is currently no comprehensive global database of foreign fighter names."
"Instead, countries including the United States rely on a patchwork system for swapping individual extremist identities," the report found, calling that system "an inherently weak arrangement that increases the odds a foreign fighter will be able to cross border(s) undetected when traveling to and from a terrorist sanctuary."
The fighters pose "a triple threat," the group wrote in a summary of its findings: "they strengthen terrorist groups, incite others back home to conduct attacks, and can return themselves to launch acts of terror."
The flow of foreign fighters is continuing to fuel the conflict in Iraq and Syria, allowing groups like ISIS to replenish their ranks even as U.S. officials assess more than 10,000 extremist fighters have been killed by U.S.-led coalition airstrikes since that bombing campaign launched in the summer 2014.
ISIS's force currently consists of between 20,000 and 30,000 fighters according to the latest CIA estimate -- mimicking the group's numbers in fall 2014.
Ranking Member Bennie Thompson, a Mississippi Democrat, called the threat of foreign fighters "clear and alarming" and said the task force's report would help focus attention on the foreign fighter issue.
"The threat of a terrorist-trained extremist returning to the United States from the battlefields in Iraq and Syria is serious, and we must do what we can to prevent it," he said.