US-backed forces have launched an offensive on ISIS’ last stronghold in eastern Syria, but the man dubbed the worlds "most wanted"-- ISIS leader Abu Bakr al-Baghdadi -- could yet again slip through the net, experts warn. There have been recurring reports of Baghdadi being killed or injured, but the elusive leader, whose only known public appearance dates to July 2014 when he proclaimed a cross-border “caliphate” in the Iraqi city of Mosul, is believed to be still alive. In August, he resurfaced in a purported new audio recording in which he urged his followers to keep up the fight despite ISIS having lost around 90 percent of the territory it held at the height of its reign of terror. He also urged them to continue waging lone-wolf attacks in the West.  Iraqi political commentator Hisham al-Hashemi, an expert on the extremist group, said his security sources told him Baghdadi was hiding out in the Syrian desert and regularly moved between al-Baaj in northwest Iraq and Hajin in Syrias southeast. As the caliphate crumbled, Iraqi forces and coalition-backed forces in Syria have killed or captured several ISIS leaders.  The US-backed Kurdish-Arab alliance launched Operation Roundup last week, the third phase of a year-old operation to clear southeastern Syria of its last ISIS holdouts, in an area around the Euphrates extending around 50 kilometers into Syria. "This is the last bastion for ISIS’ mercenaries," Zaradasht Kobani, a Kurdish commander with the Kurdish-led Syrian Democratic Forces, told AFP. "We will eliminate them here," he said. But reeling in Baghdadi will not be simple, said Hassan Hassan, a senior research fellow at the Program on Extremism at the George Washington University in Washington. "He and his group learned from previous mistakes that led to the killing of the top two leaders in 2010, (al-Baghdadis predecessor) Abu Omar al-Baghdadi, and his war minister Abu Hamza al-Muhajir," Hassan told AFP.  "This means that only a very few and highly-trusted people know where he is." The mountains, desert, river valleys and villages of the border area provide "several possible hideouts," Hassan noted. The anti-ISIS coalition may be hoping Baghdadi again gives away his whereabouts by mistake, as in November 2016 when Iraqi forces fighting to retake Mosul from ISIS picked up on a short radio exchange between him and his men. "He spoke for 45 seconds and then his guards took the radio from him," a senior Kurdish official who heard the call told Britains Guardian newspaper, which revealed the near-miss in January.  "They realized what he had done," the official added, saying the call was traced to a village west of Mosul. If Baghdadi does manage to outfox the coalition, he could join one of ISIS’ underground cells in Iraq or Syria.