Sunni-led Saudi Arabia, under Crown Prince Mohammed bin Salman, has been intensifying its confrontation with Shiite power Iran.
Saudi Arabia has accused Hezbollah of aiding Iran-allied rebels in Yemen, who fired a ballistic missile that was intercepted outside the Saudi capital earlier this month.
"Nothing justifies the failure of Prime Minister Saad Hariri to return for 12 days, therefore we consider him to be held and detained, contrary to the Vienna Convention", Aoun tweeted.
Lebanon's Christian Maronite Patriarch Bechara Boutros Al-Rai met on Tuesday in Saudi Arabia with Saad al-Hariri, who announced his resignation as Lebanon's prime minister from Riyadh on November 4, according to Saudi-owned al-Arabiya TV. He is due to hold talks with Hariri on Thursday.
5.4 magnitude natural disaster hits South Korea, tremors felt 300-km from epicentre
Analysts were monitoring "unusual seismic activity" in North Korea, the head of the nuclear test monitoring agency CTBTO said. No immediate damage was reported in the firm's steel mills.
Despite Hariri's repeated assertions that he was in Saudi Arabia of his own will and that his resignation had been his decision, Iranian President Hassan Rouhani lumped blame for the situation on Saudi Arabia, criticizing the kingdom Wednesday for its unprecedented interference in Lebanon's affairs.
France's foreign minister is expected in Saudi Arabia on Wednesday to meet with Hariri and Saudi officials. Hezbollah has said Saudi Arabia forced Hariri to resign in order to bring down his coalition government, which includes the group. However, Nasrallah has also said that he would not comment on Hariri's speech that he gave to announce his resignation because he saw it as a "Saudi statement". Hariri's father, Rafik Hariri, was assassinated in a vehicle bomb explosion in 2005, which officials believe was planted by Hezbollah agents, and Hariri said he feared the same fate.
He also expressed gratitude to Saudi Arabia for "decades of support" for Lebanon's national institutions. "You will see", Hariri wrote, without elaborating. In his statement, Hariri said he was stepping down because he feared the growing influence of Iran on Lebanon's government.
Last week, French President Emmanuel Macron announced that he had an "informal contact" with Hariri, during his visit to Dubai, adding that France did not receive any request from Lebanese ex-prime minister to come to the country.