Four men accused of plotting to send U.S. residents overseas to fight for the ISIS appear in a New York City courtroom Wednesday, April 8, 2015.

Nearly 30,000 foreigners — including at least 4,500 Westerners — have traveled to Iraq and Syria to fight with jihadists since 2011 and the United States is failing to stop Americans from joining them, a report warned Tuesday.

The document describes a national security infrastructure that is ill-equipped to deal with the myriad ways foreign militants contact and recruit Americans.

“The U.S. government lacks a national strategy for combating terrorist travel and has not produced one in nearly a decade,” states the report, which was compiled by a task force for the U.S. House of Representatives Homeland Security Committee.

“The unprecedented speed at which Americans are being radicalized by violent extremists is straining federal law enforcement’s ability to monitor and intercept suspects,” the report said.

Additionally, law enforcement tools haven’t kept pace with technological shifts, as jihadist recruiters increasingly use secure websites and apps to communicate with Americans — making it harder for law enforcement to disrupt plots and terrorist travel.

The foreign fighters that have enlisted with Islamist jihadist groups include at least 4,500 Westerners, the report states.

Of that number, more than 250 Americans have joined or tried to fight with ISIS militants.

“What keeps me up at night are the ones we’ve missed. The ones who have come back who are plotting an attack. The ones who are being radicalized over the Internet from Syria social media operatives,” Congressman Michael McCaul, a member of the Homeland Security Committee, told MSNBC.

The report states that some of the foreign fighters that flew to Syria initially did so to help oust President Bashar al-Assad, “but most are now joining the Islamic State [ISIS], inspired to become a part of the group’s ‘caliphate’ and to expand its repressive society.”

The task force report presents dozens of key findings and recommendations, and calls for an overview of the U.S. strategy to combat terrorist travel, as well better intelligence sharing domestically and with other countries.

The report also blasts security weaknesses overseas, especially in Europe.

“Pervasive overseas security gaps make it easier for aspiring foreign fighters to travel to terrorist hotspots — and increase the odds that trained jihadists will be able to travel to America undetected,” the report said.