Lebanese President Michel Aoun said earlier this week that Hariri, who abruptly announced his resignation while in Saudi Arabia on November 4, was being held hostage by Riyadh.
Adel al-Jubeir said Saudi Arabia was consulting its allies about what leverage to use against Lebanese militant group Hezbollah to end its dominance in the small Mediterranean nation and intervention in other countries.
UN Secretary-General Antonio Guterres warned Friday that a new conflict in Lebanon would have "devastating consequences" and said he was engaged in intense contacts with all players to urge de-escalation.
The head of Lebanon's powerful Hezbollah movement on Friday said Saad Hariri, who resigned as Lebanese prime minister from Riyadh last week, was "detained" by Saudi Arabia.
Saad al-Hariri resigned as prime minister on Saturday in a shock declaration read from Saudi Arabia, pitching Lebanon into deep political crisis.
Saad al-Hariri's resignation stunned Beirut's political establishment, brought down the coalition government and sparked a new political crisis.
A ceasefire took effect on Sunday in an Islamic State pocket straddling the Syria-Lebanon border, where the jihadists have been fighting the Lebanese army on one front and Hezbollah with the Syrian army on the other.
Three Lebanese soldiers were killed and one was critically wounded on Sunday when their armoured vehicle hit a landmine on the Lebanese-Syrian border, a security source said.
The leader of Lebanon's Hezbollah said on Sunday the administration of US President Donald Trump had no way to harm it, dismissing US sanctions and threats targeting his Iran-backed group.