A congressional study released Tuesday said the Obama administration has largely failed to stop more than 250 Americans who have traveled overseas since 2011 to join -- or try to join -- terror groups including the Islamic State, describing the flow of fighters as the largest global convergence of jihadists in history. 

Republicans and Democrats on the House Homeland Security Committee conducted an extensive six-month review to assess the severity of the threat from those leaving home to join jihadist groups and to identify potential security gaps. 

"It is clear that our nation faces a grave and growing threat from foreign fighters," Chairman Michael McCaul, R-Texas, said in a statement. "Sadly, global efforts have failed to stop the flow of these aspiring jihadists into Syria, and we have already seen 'returnees' from the conflict zone come home to America and Europe and plot acts of terror. Even more, those still on the battlefield are radicalizing their peers online and inciting them to launch homegrown attacks." 

According to the final report, of the hundreds of Americans who have sought to travel to Syria and Iraq, authorities have only interdicted a fraction of them. 

"As horrible as attacks like the Chattanooga shooting were, we've been incredibly lucky," National Security Analyst for the Clarion Project Professor Ryan Mauro told Fox News. "But our luck is bound to run out." 

The report also reflects on the 10,000 foreign fighters that battled the Soviets in Afghanistan in the 1980s, contributing to the rise of Al Qaeda. Today, more than 25,000 have joined jihadists in Iraq and Syria. 

"If the fighting in Afghanistan brought us 9/11, it's frightening to think what the fighting in Syria and Iraq will bring us," Mauro said. 

The report also said the Obama administration lacked a strategy to identify all who try to return to commit terror attacks, saying: "Several dozen have also managed to make it back into America." It noted that several people were identified and arrested this year trying to return to the United States. 

Key findings in the report are: 

  • "Despite concerted efforts to stem the flow, we have largely failed to stop Americans from traveling overseas to join jihadists. Of the hundreds of Americans who have sought to travel to the conflict zone in Syria and Iraq, authorities have only interdicted a fraction of them." 
  • "The U.S. government lacks a national strategy for combating terrorist travel and has not produced one in nearly a decade." 
  • "Gaping security weaknesses overseas-especially in Europe-are putting the U.S. homeland in danger by making it easier for aspiring foreign fighters to migrate to terrorist hotspots and for jihadists to return to the West." 

"The Task Force's report was done in a bipartisan manner and provides bipartisan proposals," said Democratic Lead, Rep. Loretta Sanchez, D-Calif. "These are real threats, requiring real solutions and commitments. Moving forward, it is critical that we continue to tackle this problem together in order to facilitate action and progress." 

Fox News' Brooke Singman and The Associated Press contributed to this report.