Lebanon's president on Monday appealed for the country's political factions to remain united to face off any fallout from Prime Minister Saad Hariri's shock resignation.

Hariri announced he was leaving his post in a television broadcast at the weekend from Saudi Arabia, where he met King Salman on Monday.

The surprise statement sparked concerns that Lebanon would be sent into a political tailspin, but President Michel Aoun sought to allay those fears on Monday.

Speaking to senior national security officials at the presidential palace, Aoun said Lebanon's political leadership had responded positively to "calls for calm".

"National unity remains the foundation for maintaining security and political stability in the country. All efforts should concentrate on preserving this unity, especially in the circumstances that the country is passing through," Aoun said.

Top officials in the meeting included Lebanon's defence and interior ministers, as well as the heads of the army and general security service.

After the meeting, Justice Minister Salim Jreissati said Aoun would not take any decisions before meeting with Hariri, according to the presidency.

It remains unclear when Hariri will return to Lebanon from Saudi Arabia, where he was meeting with King Salman and other Saudi officials on Monday.

The state-run Saudi Press Agency said the two leaders "reviewed the situation in Lebanon," without providing additional details.

- 'Do not worry' -

Hariri is a two-time premier whose father Rafiq held the same position for years and was assassinated in 2005.

In his televised resignation on Saturday, he accused Iran and its Lebanese ally Hezbollah of taking over his country and destabilising the broader region.

His statement prompted fears that Lebanon -- split into rival camps led by Hariri and powerful Shiite movement Hezbollah -- would be caught up in spiralling tensions between Riyadh and Tehran.

Hezbollah chief Hassan Nasrallah sought to downplay the risks of conflict between Lebanon's rival camps, or with his party's arch-foe Israel.

"Do not listen to alarmist speeches... do not worry, there is nothing to worry about," he said in a televised address on Sunday night.

"We will react responsibly and calmly... we are concerned about the security" of Lebanon, Nasrallah added.

Nasrallah said his party had not sought Hariri's resignation, which had instead been "imposed" on the premier by Saudi Arabia.

He also called for "calm, patience and waiting until the reasons become clear" for Hariri stepping aside.

- 'Whole country at stake' -

But Sami Atallah, executive director of the Lebanese Center for Policy Studies, said there was a real risk the country could descend into a fresh cycle of violence.

"The whole country is at stake. The whole political system is at stake," Atallah told AFP on Monday.

With no obvious contender as the future prime minister, the political uncertainty could shake international confidence in Lebanon's economy, he said.

"Are they (the leaders) going to be able to rise to the occasion, build the bridges, stop the political bickering, put their differences apart, and realise the gravity of the situation we are in?"

In the wake of Hariri's resignation, Lebanon's ministers will operate in a "caretaker" role until Aoun names a new prime minister who will then appoint new ministers. The process typically takes months of political wrangling.

The fresh political turmoil will also likely impact long-awaited legislative elections expected to be held in May, the first in nine years after parliament repeatedly extended its own term.

Atallah said it appeared likely that Hariri's resignation was part of the wider internal shakeup in Saudi Arabia, where 11 princes, four sitting ministers and dozens of former ministers have been arrested.

"It's very hard to believe that it's a coincidence that the prime minister resigns in Riyadh the same evening during which these arrests take place," he said.

Source: AFP