In Yemen, fierce clashes in the last major northern stronghold for the internationally recognized government could mark a turning point in the deadly six-year conflict. The oil-rich city of Marib is now at the center of a military escalation by Iran-backed Houthi rebels attempting to extend their control of the country further east with a devastating campaign of drone and missile attacks on both Yemen and Saudi Arabia. Saudi-backed government forces say US president Joe Biden's decision to reverse Trump's widely criticized designation of the Houthis as a terrorist group has only emboldened the rebel group. CNN's Nic Robertson gained access to Marib's frontline, where the battle for control in the ancient desert city is raging on.