A homemade explosive device that went off during a patrol in a Shia town also wounded two soldiers, the Saudi interior ministry said in a statement, describing it as a "terrorist incident."
An explosion has killed a soldier and wounded two more in Saudi Arabia's eastern Qatif province, the interior ministry said on Monday.
The homemade explosive device went off during a patrol in the Shia town of Awamiya on Sunday evening, the ministry said in a statement carried by the state news agency.
Major Tariq al Alaqi was killed in the blast, the ministry said, describing it as a "terrorist incident."
Soldiers were patrolling the town's Almosara neighbourhood, where unrest has escalated in recent weeks around a redevelopment project in the old district.
Alaqi is at least the fourth person to have been killed in the violence.
The interior ministry has said criminals involved in drugs and arms trade were implicated in the unrest.
Last month, gunmen killed two civilians and a rocket-propelled grenade left a policeman dead in the area.
The UN has urged the kingdom to halt demolition of the 400-year-old Almosara district, which it says has caused "injury, deaths and material losses to the civilians."
Awamiya has seen repeated security incidents in recent years, following protests that began in 2011.
Most of Saudi Arabia's Shia community live in the eastern province and have long complained of marginalisation in the Sunni-ruled kingdom.