WASHINGTON — The U.S. is losing the battle to stop Americans from traveling abroad to enlist in ISIS, a bipartisan congressional task force concluded in a report released Tuesday.

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, foreign fighters have swelled the ranks of those radical militant groups waging war and committing atrocities in Iraq and Syria by more than 7,000. 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.”

The report’s release Tuesday comes as President Barack Obama is chairing a summit at the United Nations on how to counter ISIS and the threat of extremism worldwide.

Federal officials 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.

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 the border 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.