Saudi Arabia has ordered its citizens out of Lebanon amid skyrocketing tensions between their two governments.

A brief statement carried by the state-run Saudi Press Agency called on all Saudis living in or visiting Lebanon to depart, and warned against travel to the country.

"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, a Saudi Foreign Ministry source quoted by the agency said.

Lebanese Prime Minister Saad Hariri shocked his country Saturday when he announced in a televised statement out of Saudi Arabia that he was resigning. He has not been seen in Lebanon since.

He said his country had been taken hostage by the militant group Hezbollah, a partner in his coalition government and a major foe of Saudi Arabia. Saudi Arabia says it considers Hezbollah's participation in the Lebanese government an "act of war" against the kingdom.

Lebanese President Michel Aoun has said he will not consider the premier's resignation until the two meet in person.

Also on Thursday, Mr Hariri's political party called for his immediate return to Lebanon.

Following a meeting of his Saudi-aligned Future Party in Beirut on Thursday, the party issued a statement saying it was "necessary" for Hariri to return "to restore Lebanon's dignity and respect."

The statement read by former Prime Minister Fuad Saniora seemed to indicate that Mr Hariri is being held in Saudi Arabia against his will.

Mr Hariri resigned his post abruptly on Saturday in a strange, pre-recorded speech.

In his absence, Lebanon has been awash with speculation the 47-year old prime minister may be held against his will in Saudi Arabia. Saudi officials have denied Mr Hariri is under house arrest.

AP and Reuters