The head of Lebanon's militant group Hezbollah says the country's prime minister, Saad Hariri, was forced by Saudi Arabia to resign.

Hezbollah leader Hassan Nasrallah in a speech Sunday urged patience after Hariri resigned suddenly in a televised address from the Gulf kingdom a day earlier. 

Hariri is not believed to have returned to Lebanon, and Lebanese President Michel Aoun will not accept Hariri's resignation until he returns to Lebanon to explain his reasons, palace sources said on Sunday, delaying for now the politically difficult consultations over his successor.

Nasrallah accused Saudi Arabia of drafting Hariri's resignation letter and forcing him to read it on Saudi TV. He even asked whether Hariri is being held against his will.

Aides to Hariri, whose family made their fortune in the Saudi construction industry, strongly denied he had been detained or had been forced to resign.

Lebanon Iran

Former Lebanese prime minister Saad Hariri resigned from his post Saturday during a trip to Saudi Arabia, in a surprise move that plunged his country into uncertainty amid heightened regional tensions. (Hussein Malla/The Associated Press)

Nasrallah's broadsides against Saudi Arabia have only grown harsher as the rivalry deepens between the Gulf kingdom and Iran over wars in Syria and Yemen. Hezbollah, which has sent thousands of its men to fight in Syria, is supplied and financed by Iran and seen as its proxy in Lebanon.

Bahrain imposes travel ban on Lebanon

In neighbouring Bahrain, the government on Sunday ordered its citizens in Lebanon to "leave immediately" and banned travel to Lebanon. Bahrain is a bellwether nation for the Saudi Arabia-dominated Gulf Cooperation Council and often the first to announce sanctions and travel bans, usually targeting countries seen as close to Iran.

Hariri became prime minister in late 2016 in a coalition government that included the Shia militant group Hezbollah, one of Saudi Arabia's chief detractors in the region. He could not have formed a government without the group, which operates its own militia freely in Lebanon.

Hezbollah and its allies have been given veto power in Lebanese politics since Hezbollah forces seized the streets of Beirut in brief clashes in 2008. Their political bloc controls the largest share of seats in Lebanon's parliament.

Hezbollah was founded with Iranian support in 1982 to resist the Israeli invasion of Lebanon and has since emerged as a regional power in its own right. 

It is fighting alongside Iranian advisers and militias in the civil war in neighbouring Syria, providing crucial support to
President Bashar al-Assad's forces as a crackdown on anti-government demonstrations morphed into full-fledged war.

Dozens of rebel factions in Syria are or have been backed by Turkey, Saudi Arabia, and Saudi Arabia's Gulf allies.

Lebanon, once one of the key flashpoints of the Saudi-Iran rivalry, officially declared itself neutral with respect to the
Syrian war. But Hezbollah fighters poured into Syria, angering Saudi Arabia.

Assad and his Iranian-supported allies are now firmly in command of the war in Syria, in a humiliation to Saudi Arabia and the Gulf.

With files from Reuters