Saudi Arabia has ordered its citizens visiting or living in Lebanon to leave the country.
Saudis have also been warned against travelling to Lebanon, as tensions reach boiling point between the two nations.
The kingdom's official news agency (SPA) quoted an official source in the foreign ministry as saying: "Due to the circumstances in the Lebanese Republic, the kingdom asks its citizens who are visiting or residing" in the country to leave it as soon as possible.
It comes after a surprise resignation from Lebanese Prime Minister Saad Hariri on Saturday, in a televised statement from the Saudi capital. Riyadh.
He said his life in Lebanon was in danger and the climate in his country felt similar to the time leading up to the assassination of his father, prime minister Rafik Hariri, in 2005.
"I have sensed what is being plotted covertly to target my life," he said.
Mr Hariri said his country was being held hostage by the Shia Muslim militant group Hezbollah, a partner in his coalition government, and an enemy of Saudi Arabia, which considers its involvement in the Lebanese government as an "act of war".
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He also attacked Iran, saying Hezbollah and Iran are meddling in Arab affairs.
Mr Hariri was appointed prime minister in late 2016 and was leader of a 30-member national unity cabinet that included Hezbollah.
The country is largely divided between those loyal to Saudi Arabia, led by Sunni Muslim Mr Hariri, and those loyal to Iran and Hezbollah.
Mr Hariri's Future Party has suggested he is kept in Saudi Arabia against his will and has called for his immediate release.
In a statement the party said it was "necessary" for Mr Hariri to return "to restore Lebanon's dignity and respect".
Saudi officials have denied the 47-year-old is being held against his will.
The travel restriction coincides with other power moves by the young heir to throne, Prince Mohammed bin Salman, who has ordered the detention of hundreds of people including 11 billionaire princes in a ballroom in the five star Ritz-Carlton in Riyadh.
It's said to be a move by the Saudi Crown Prince to consolidate his power as part of plans to reform and modernise the kingdom.