Lebanese Prime Minister Saad al-Hariri resigned from his post Saturday during a trip to Saudi Arabia in a surprise move that plunged Lebanon into uncertainty amid heightened regional tensions.

In a televised address from Riyadh, Saudi Arabia, Hariri fired a vicious tirade against Iran and its Lebanese proxy Hezbollah group for what he said was their meddling in Arab affairs and said "Iran's arms in the region will be cut off."

"The evil that Iran spreads in the region will backfire on it," Hariri said, accusing Tehran of spreading chaos, strife and destruction throughout the region.

Hariri was appointed prime minister in late 2016 and headed a 30-member national unity cabinet that included the Shiite militant Hezbollah. The government has largely succeeded in protecting the country from the effects of the civil war in neighbouring Syria.

'The evil that Iran spreads in the region will backfire on it.' - Saad Hariri

The country is sharply divided along a camp loyal to Saudi Arabia, headed by the Sunni Muslim Hariri, and a camp loyal to Iran represented by Hezbollah. Lebanese President Michel Aoun, who was elected in October 2016 after more than two years of presidential vacuum, is a close ally of Hezbollah.

Aoun's election was made possible after Hariri endorsed him for president, based on an understanding that Aoun would then appoint Hariri as prime minister.

In a statement, the presidential office said Aoun was informed by Hariri in a phone call of his resignation, adding that the president now awaits Hariri's return to Lebanon to clarify the circumstances of his resignation.

Hariri's bombshell resignation Saturday was expected to raise tensions in the country and ushers in a stage of deep uncertainty and potential instability. It comes amid a sharp escalation in Saudi rhetoric against its regional archrival, Iran.

Middle East expert Fawaz Gerges told CBC News Saturday that tensions could turn violent. 

"There is a real danger that the tensions between the Hariri-dominated faction and Hezbollah-dominated faction could easily escalate into an armed confrontation," said Gerges, who is chair of contemporary Middle Eastern studies at London School of Economics.

"The Saudi Arabia-Iranian rivalry now is going to play out on Lebanon's streets in the next few days and next few weeks."

Father assassinated 12 years ago

In his speech, Hariri suggested he feared for his life and said the climate in the country is similar to the one that existed before his father, the late prime minister Rafik Hariri, was assassinated in 2005.

LEBANON-HARIRI/

In this file photo from 2015, people stand in front of an image of Rafik al-Hariri as they mark the 10th anniversary of the former prime minister's assassination near his grave in downtown Beirut. (Jamal Saidi/Reuters)

Several Hezbollah members are being tried in absentia for the killing by a UN-backed tribunal in The Hague, Netherlands. Hezbollah denies any involvement.

Hezbollah has sent thousands of its fighters to Syria to shore up President Bashar al-Assad's government. The group's intervention in Syria is highly controversial in Lebanon.

Hariri said Hezbollah's policies have put Lebanon "in the eye of the storm." His attacks on Hezbollah come on the heels of new U.S. sanctions on the group that many fear will negatively affect the Lebanese economy.

"Hezbollah was able in past decades to impose a reality in Lebanon by force of arms directed at the chests of Syrians and Lebanese," he said.

'Will of the Lebanese is strong'

"I declare my resignation from the premiership of the Lebanese government, with the certainty that the will of the Lebanese is strong," Hariri said.

"When I took office, I promised you that I would seek to unite the Lebanese, end political division and establish the principle of self-sufficiency, but I have been unable to do so. Despite my efforts, Iran continues to abuse Lebanon," he said.

Hariri's words are explosive, said Gerges. "He says that Hezbollah now controls the state in Lebanon. He says that Iran now dominates Lebanon and the Arab neighbourhood. These are major, major accusations."

Earlier this week, Saudi State Minister for Gulf Affairs Thamer al-Sabhan sharply criticized Hezbollah, calling for its "toppling" and promising "astonishing developments" in the coming days during an interview with the Lebanese TV station MTV.

Sabhan met with Hariri in Saudi Arabia when the now resigned prime minister was visiting earlier this week. Hariri abruptly returned to the kingdom later Friday before his bombshell announcement Saturday.

In tweets after meeting Hariri, al-Sabhan described it as "long and fruitful meeting" that resulted in agreements over many issues that concern the Lebanese. "What's coming is better, God willing," Sabhan tweeted on Tuesday. In a series of tweets, Sabhan criticized the Lebanese government for tolerating Hezbollah's criticism of the kingdom.

He earlier said that those who cooperate with Hezbollah must be "punished."