Editor's note: The videos embedded in this story contain offensive language. Please use caution in viewing.
WASHINGTON – The Federal Bureau of Investigation is becoming increasingly alarmed over the prospect that Americans now carrying out wartime attacks alongside Islamic militants in Syria – and they are said to number at least 50 – could return to their U.S. homeland and pose a threat.
FBI counter-terrorism officials told WND the American jihadis who survive the battlefield in Syria are unknown and could return to America without even being detected.
Syrian sources have told WND that at least 25 American fighters are in Syria now, with others working in Turkey. Photos shown to WND reveal a group of American jihadists actively working alongside Syrian opposition fighters, some of whom are linked to al-Qaida's Jabhat al-Nusra Front.
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The Americans, along with fighters from European countries, seek to topple the regime of Syrian President Bashar al-Assad, with many joining the ranks of al-Nusra. Al-Qaida and its affiliates, along with other Islamic militant groups, want to set up Islamic caliphates that encompass not only Syria but also Lebanon and Iraq.
The terror-linked groups also recently have returned to Iraq and taken over entire cities in the Sunni-dominated Anbar province, including Ramadi and Fallujah, where U.S. Marines fought and died in bloody battles.
Video shows Americans fighting in Syria. In one case, a video shows an American in a Jeep bragging about having shot down a Syrian military helicopter.
Warning: Offensive language.
"Yes, we smoked the m----- f------, didn't we," the American is heard to be saying as the video then shows his full face. "We smoked about – I don't know – about 10 or 20."
Another video shows the same American telling Assad that his "days are numbered, you're going down in flames."
"You should just quit now while you can and leave," the American says, surrounded by other bearded jihadists.
"You're going to die no matter what. Where you go, we will find you and kill you."
Warning: Offensive language.
The American in the videos was identified as Eric Harroun, an American Muslim convert from Phoenix, Ariz., and a former fighter with the Free Syrian Army and al-Nusra. He was in the U.S. Army from 2000 to 2003 but sustained a serious head injury from a crash in Fort Riley, Kan.
Following visits to Lebanon in 2010 and Egypt in 2011, when he was arrested for his involvement in pro-democracy demonstrations in Tahrir Square, he then visited Turkey in November 2012.
In January 2013, he made his way into Syria and joined a faction of the Free Syrian Army followed by a month's stint with al-Nusra. He then was sent to Turkey to pick up weapons but decided to stay there and returned to the U.S. in March 2013.
Because of his well-publicized statements, he was detained from late March to September 2013 by the FBI. Harroun in an affidavit allegedly told the FBI that he hated al-Qaida and didn't know any members.
Although he originally was charged with using weapons of mass destruction outside the U.S., Harroun plea-bargained to a count violating a law regulating munitions exports. A federal court in Arizona sentenced him to time served and released him last September.
Analysts say American jihadists seeking to return to the United States probably would go through the international airports in Istanbul, Turkey, where Sunni opposition fighters in Syria or Beirut, Lebanon, are supported.
If they do so, they probably would be allowed entry without a challenge, as long as there is no reference to them having been in Syria.
WND is aware that Americans returning from both countries are routinely cleared by agents of U.S. Customs and Border Protection without a challenge.
The increased concern expressed by U.S. law enforcement and counter-terrorism officials mirror similar concerns from Congress members and national security counterparts in other Western countries such as Britain and Canada.
"We know that American citizens as well as Canadian and European nationals have taken up arms in Syria, Yemen and in Somalia," said Sen. Thomas Carper, D-Del. "The threat that these individuals could return home to carry out attacks is real and troubling."
Matthew G. Olsen, head of the National Counterterrorism Center, or NCTC, also carries the load of worry.
"Many homegrown violent extremists lack advanced operational training, which forces them to seek assistance online from like-minded extremists or pursue travel to overseas jihadist battlegrounds to receive hands-on experience," Olsen said.
"Recent political unrest in many parts of North Africa and the Levant, including in Syria, affords HVEs (homegrown violent extremists) opportunities to join militant groups overseas," Olsen said. "Foreign terrorist groups could leverage HVEs to recruit others or conduct operations inside the U.S. or overseas."
The new U.S. Homeland Department secretary, Jeh Johnson, similarly has expressed concern about the prospect of American jihadists returning home.
"Based on our work and the work of our international partners, we know individuals from the U.S., Canada and Europe are traveling to Syria to fight in the conflict," Johnson said.
FBI Director James Comey recently expressed concern that Syria could become a repeat of Afghanistan in the 1980s, where foreign fighters were attracted to the country following the Soviet invasion.
"Only the Afghan insurgency against the Soviet Union in 1979-89 compares with Syria in terms of the number of foreign fighters," Comey said. "An in-depth study by Norwegian scholar, Thomas Hegghammer, in the journal International Security in late 2011 estimated that 5,000 to 20,000 foreign fighters had traveled to Afghanistan between 1980 and 1992.
"As such," he said, "the arrival of 5,000 to 10,000 foreign fighters in Syria in only 18 months appears highly significant."
Eventually, those fighters will return to their homes in Europe and the U.S.
"At some point all of these people from Europe are going home," said Rep. Mike Rogers, R-Mich., chairman of the House Permanent Select Committee on Intelligence. "All the folks there from all over the world, including the United States, will be coming home if they do not meet their end on the battlefield."