Saudi Arabia, the United Arab Emirates and Kuwait have advised their citizens not to travel to Lebanon and urged those who are in the country to leave as soon as possible.

Saudi Arabia's official news agency SPA quoted a source in the foreign ministry on Thursday as saying: "Due to the situations in the Republic of Lebanon, the official source at the Ministry of Foreign Affairs stated that the Saudi nationals visiting or residing in Lebanon are asked to leave the country as soon as possible.

"The Kingdom advised all citizens not to travel to Lebanon from any other international destinations."

Only hours later, Kuwait and the UAE also urged its nationals to leave Lebanon immediately.

Bahrain - an ally of Saudi Arabia - had already ordered its citizens to leave Lebanon on Sunday, with the Bahraini foreign ministry issuing a travel advisory that cited "safety considerations".

Leave of absence

Lebanon has been on edge after the sudden resignation of Prime Minister Saad al-Hariri, who announced his departure while on a visit to Saudi Arabia on Saturday.

His whereabouts have since been unknown. However, officials told Al Jazeera on Thursday that Hariri may be under house arrest or temporarily detained in the Saudi capital of Riyadh.

Lebanon's Future Movement party, which is headed by Hariri, demanded on Thursday that the prime minister returns from the kingdom immediately in its sharpest statement yet over his leave of absence.

"The return of the Lebanese prime minister, the national leader, Saad al-Hariri, and the head of the Future Movement, is necessary to restore the dignity and respect to Lebanon at home and abroad," said a former prime minister, Fouad Siniora, in a statement read on TV.

Al Jazeera's correspondent in Lebanon said that the country's President, Michel Aoun, would soon call for assistance from the international community, the Arab League, the United States, the United Kingdom, China and Russia - to help uncover the reason behind Hariri's unexpected resignation.

Reuters news agency reported on Thursday, citing a senior Lebanese official, that the Lebanese government has not received Hariri's official resignation papers, and as such still considers him as prime minister. The official added that the restrictions imposed by Saudi Arabia act as an "attack on Lebanon's leaders".

Riyadh has denied that the prime minister is under house arrest.

'War declaration'

In his November 4 resignation, Hariri implicitly blamed Iran and its Lebanese ally, Hezbollah, for his decision. In his speech, he said that he suspected there were plans to target his life.

His father, Rafik Hariri - who also served as prime minister - was killed by in a bomb attack in 2005. Many of Hariri's supporters blamed the bombing on Hezbollah, which denies it was involved.

In his address from Riyadh, Saad al-Hariri said Iran planted "disorder and destruction" in the country and meddled in the internal issues of Lebanon as well as other Arab countries.

Referring to Hezbollah, which is backed by Iran, Hariri said, "Iran's arm ... has managed to impose a fait accompli on Lebanon through the power of its weapons" in the last few decades.

"They have built a state within a state," Hariri said from Riyadh.

His unexpected move also stoked fears of an escalation in the regional divide between Iran and the Gulf states, primarily Saudi Arabia, with Lebanon on the front lines.

Thamer al-Sabhan, the Saudi minister for Gulf affairs, said on Monday that Lebanon's government would "be dealt with as a government declaring war on Saudi Arabia" because of what he described as "acts of aggression" committed by Hezbollah.

In an interview with Al Arabiya, Sabhan said Hezbollah was involved in every "terrorist act" that threatened Saudi Arabia.

"The Lebanese must choose between peace or aligning with Hezbollah," he added, without offering details about what action Riyadh might take against Beirut.

Hariri, a leading Sunni politician, has been in office for less than a year, but previously served as prime minister between 2009 and 2011.