Residents of Riyadh reported seeing flames and a column of black smoke near King Khalid International Airport on Saturday, hours after Saudi authorities warned people in parts of the country of possible danger. The alert advised residents to remain indoors and stay away from windows, according to Saudi Civil Defense.

Video shared on social media appeared to show smoke rising from the airport. Flight-tracking service Flightradar24 said the airport was experiencing “major problems,” although the supplied report did not specify whether those problems were caused by the reported fire or by another incident.

An AFP journalist reported seeing firefighters working to extinguish a burning fuel truck close to the site. The source material does not identify the cause of the fire, say whether the airport was struck, or report casualties or damage.

Saudi Civil Defense later issued an all-clear. A 27-year-old resident in northern Riyadh told AFP that they heard the alarm and felt their windows shake, describing the experience as frightening.

The incident occurred amid an increase in reported attacks by Yemen’s Houthi rebels, who declared a naval blockade of Saudi Arabia in July, according to the source. The Houthis have since increasingly targeted Saudi cities and shipping, the report said, while Saudi Arabia has carried out strikes against the group.

The developments have added to tensions around the Red Sea and the Bab al-Mandab Strait. UN Assistant Secretary-General Khaled Khiari said earlier this week that efforts were urgently needed to prevent Yemen’s conflict from threatening the security of the maritime route, and called for sustained engagement to reduce tensions, prevent escalation and protect freedom of navigation.