Rasmussen will tell the committee that at least 3,400 of the foreign fighters in Syria came from Western countries.

The number of foreign fighters traveling to join the Islamic State of Iraq and Syria (ISIS) or rival militant groups in Syria is continuing to grow, a senior U.S. counterterrorism official will tell a congressional hearing on Wednesday.

The United States and its allies believe that more than 20,000 foreign fighters from more than 90 countries have gone to Syria, Nick Rasmussen, director of the National Counterterrorism Center, said in testimony prepared for a hearing of the House of Representatives Committee on Homeland Security.

A senior intelligence official said this compared to an estimate of “more than 19,000” foreign fighters which the U.S. government produced in mid-January.

However, the flow of fighters to Syria is irregular, and the rise in the estimate does not mean that hundreds of new foreign fighters were pouring into Syria every week, said the official, who spoke on condition of anonymity.

Rasmussen will tell the committee that at least 3,400 of the foreign fighters in Syria came from Western countries, and that they include over 150 U.S. citizens or residents. A copy of his testimony was made available to Reuters.

He says the “majority” of those arriving in Syria now are joining ISIS formations in Syria and Iraq.

In other testimony prepared for Wednesday’s hearing, the Homeland Security department’s intelligence chief, Francis X. Taylor, said the United States remains “unaware of any specific, credible imminent threat to the Homeland.”

However, Michael Steinbach, assistant director of the FBI, intends to say that last month ISIS released a video encouraging “lone wolf” militants to attack soldiers, police and intelligence officers in Western countries.

[wpResize]