Intelligence agencies now believe that as many as 150 Americans have tried and some have succeeded in reaching in the Syrian war zone, officials told the House Homeland Security Committee in testimony prepared for delivery on Wednesday. Some of those Americans were arrested en route, some died in the area and a small number are still fighting with extremists.
Nick Rasmussen, chief of the National Counterterrorism Center, said the rate of foreign fighter travel to Syria is without precedent, far exceeding the rate of foreigners who went to wage jihad in Afghanistan, Pakistan, Iraq, Yemen or Somalia at any other point in the past 20 years.
US officials fear that some of the foreign fighters, who come from 90 countries, will return undetected to their homes in Europe or the US to mount terrorist attacks.
At least one of the men responsible for the attack on a satirical magazine in Paris had spent time with Islamic extremists in Yemen.
Also at the White House, President Barack Obama praised Kayla Jean Mueller, the young American whose death was confirmed yesterday.
Mueller died while in Islamic State hands, though the group blamed a Jordanian airstrike, and Obama said, "No matter how long it takes, the United States will find and bring to justice the terrorists who are responsible for Kayla's captivity and death."
As for foreign fighters, officials acknowledge it has been hard to track the Americans and Europeans who have made it to Syria, where the Islamic State group is the dominant force trying to overthrow the government of President Bashar Assad.
The 20,000-fighters estimate is up from 19,000, Rasmussen will tell the House committee, according to prepared testimony. The number of Americans or U.S. Residents who have gone or tried to go is up to 150 from 50 a year ago and 100 in the fall.