Saudi Arabia's eastern province has seen a number of militant shootings and bombings of on and off-duty police and troops.
Awamiya and other parts of the Shia-majority eastern province have been shook by a wave of protests against the government.
At 18.08hrs the aircraft took off for the final leg to Jeddah. after take-off, while climbing to FL350, visual and aural warnings indicated smoke in the aft cargo compartment C-3.
Climbing through FL220 (at 18.20h), a return to Riyadh was initiated.
Saudi Arabia has come under huge criticism for its campaign in the eastern province, which has led to scores of civilians dead, including a three-year-old child on Wednesday.