ISIS fighters in Syria (file)
ISIS fighters in Syria (file)Reuters

Hundreds of Americans have traveled to Iraq and Syria to fight for ISIS and around 50 have returned to America, a senior US lawmaker said Sunday.

That's the kind of scenario that led to the massacres in Paris terror on November 13, said Republican Congressman Michael McCaul, chairman of the House Homeland Security Committee.

"And the Paris attacks were the classic case of the foreign fighter," McCaul told CNN, referring to a Syrian passport found near the body of one of the Paris attackers. The massacre left 130 dead and hundreds wounded.

"We've had hundreds of them travel over there and 50 have come back to the United States," the congressman added.

More than 70 ISIS supporters were arrested in the United States last year and investigations are underway in all 50 states, he noted, according to AFP.

McCaul said US intelligence officials are also very concerned about the possibility of an insider job leading to a bomb being placed on a US-bound airliner.

He said this is what happened with the Russian airliner that exploded over Egypt on October 31, killing all 224 people aboard. ISIS responsibility.

"Someone was compromised or radicalized or perhaps bribed to put a piece of luggage, a bomb on the airplane. That is, a worker at the airport," the congressman said.

That kind of threat is hard to stop, no matter how good a country's screen technology is, AFP noted.

"That kind of scenario playing on an airliner flying directly into the United States is what I'm most concerned about," McCaul added.

Another lawmaker, Republican Richard Burr, chairman of the Senate Intelligence Committee, said Sunday there is currently no credible, specific threat of a terror attack against the United States.

But over the past year, there have been more "threads of threats" in America and elsewhere in the world than any other year since the September 11, 2001 attacks in the United States.

"So the risk remains high," Burr said.

He also said of ISIS that "to talk about containment is really a joke."

"The reality is that ISIS may be geographically contained in Syria and Iraq, but their efforts around the world to project terrorism and to commit terrorism is as robust today as it's ever been," Burr said.

Terrorist 'came through Greece'

A Syrian passport found by police at the scene of the mass shooting in a Paris concert hall belonged to an asylum seeker who registered on a Greek island in October, a Greek minister said the day after the massacre.

"We confirm that the Syrian passport holder came through the Greek island of Leros on October 3 where he was registered under EU rules," said a statement issued by Nikos Toskas, the minister for citizen protection.

French police said the document was found "near the body of one of the attackers" in the investigation into the main Paris attack, at the Bataclan concert hall, where 82 people were killed. That attacks was one of six coordinated shootings and suicide bombings.

Soda can IED

In a recent issue of its magazine, Dabiq, ISIS published a photo explaining how its terrorists brought down the Russian airliner. 

The image, tagged "Exclusive," shows an IED (improvised explosive device) and the soda can it was hidden in before the bombing. 

"After resolving to bring down a plane belonging to a nation in the American-led Western coalition against ISIS, the target was changed to a Russian plane," the group wrote. 

"A bomb was smuggled onto the airplane," the group added, noting it had "discovered a way to compromise the security at Sharkm el-Sheikh airport" to bring down the Metrojet airliner on October 31. 

AFP contributed to this report