While covering the rebellion in Syria last week, ABC's Alexander Marquardt reported on a new threat inside the embattled country. In his report Monday night on "World News with Diane Sawyer," Marquardt cites a "much more ominous presence" in Syria, one that has many in Washington worried - "foreign fighters, mostly religious fundamentalists, streaming in - taking up the fight. They want Assad to go and Syria to become an Islamic state. We headed out to find some of them, instead… they found us. They were heavily armed so we hid our camera."

After the off-camera exchange Marquardt notes "we were stopped by a van full of what were clearly fundamentalist fighters. They stopped our car, they all had AK-47s, they wanted to see our passports and IDs - clearly very unhappy to see us. What was quite interesting is they were speaking Arabic with a non-Syrian accent as well as other languages. So we got out of there really fast."

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In addition to the arrival of foreign fighters there is something else even more worrying in Syria - "the growing number of suicide bombings is evidence that al Qaeda is here as well," Marquardt reports. "Travelling the country it becomes clear that Syria is becoming more chaotic - making the question of who would take over after Assad all the more complicated and possibly more dangerous," he says.

Watch Marquardt's Full "World News" Report: