WASHINGTON (AP) - The government has largely failed to stop more than 250 Americans who have traveled overseas to join or tried to join terrorist groups, including the Islamic State group, a new congressional study concluded on Tuesday.

"The United States joins with the worldwide community to urge all parties in Iraq and Syria and the global community to respect and protect archaeological, historic, religious and cultural sites, including museums and archives, and reaffirm that all those who destroy important cultural property must be held accountable", the State Department said in its release.

More than 25,000 foreigners have flocked to Syria and Iraq since 2011 to fight with ISIS and other Islamist terrorist groups, according to US estimates.

"As terrible 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. The foreign fighter travel to the region has increased greatly. Among European nations, Britain emerged as the highest supplier of jihadi, with more than 1000 Britishers travelling to Iraq and Syria, and turning militants.

As of July, the IS - also identified as Daesh, ISIS and ISIL - has brought in $8 million to $10 million dollars each month through its smuggling of oil and gas throughout Iraq and Syria.

It did not provide details on the several dozen who have sneaked back into the United States without being arrested or monitored. It noted that several people were identified and arrested this year trying to return to the United States.

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. "Moving forward, it is critical that we continue to tackle this problem together in order to facilitate action and progress".