TEHRAN – Saudi Arabia has framed its national security as a “red line,” warning it will act decisively against any foreign military support for separatist groups in Yemen. The declaration on Tuesday came hours after Saudi-led coalition airstrikes targeted vehicles and cargo at Mukalla port, which Riyadh said had been supplied by the United Arab Emirates to the Southern Transitional Council (STC). Though the strike was limited and caused no casualties, its political significance was profound: Saudi Arabia is signaling that Abu Dhabi’s maneuvers have crossed into confrontation.