Lebanon's president appealed to Saudi Arabia on Saturday to explain why Saad Hariri had not returned to Beirut since his surprise resignation as prime minister a week ago.

Hariri announced on November 4 in a televised statement from Riyadh that he would be stepping down from his post, shocking the Lebanese political class.

The premier has yet to return to Lebanon and rumours have swirled that he was being held in Saudi Arabia against his will.

President Michel Aoun on Saturday called on the kingdom to “clarify the reasons that have prevented the return of PM Hariri to Lebanon to be among his people and supporters.”

Aoun has yet to formally accept Hariri's resignation and has criticised the circumstances surrounding it as “unacceptable.”

In his shock announcement, Hariri 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 Hezbollah — would be caught up in spiralling tensions between Riyadh and Tehran.

And after a week outside Lebanon, rumours have circled that Hariri — who also holds Saudi nationality — is under de facto house arrest in the kingdom.

“The head of the Lebanese government is detained in Saudi Arabia, he is banned from returning to Lebanon until now,” Hezbollah chief Hassan Nasrallah said in a televised address on Friday.

Members of Hariri's own Al-Moustaqbal (Future) party said they had no information on his fate.

And Lebanese Foreign Minister Gebran Bassil announced on Friday he was launching a “diplomatic campaign to bring back the head of our government of his own free will.” Even world powers have appealed for calm and Hariri's freedom of movement.

United States Secretary of State Rex Tillerson on Friday described Hariri as “a strong partner” and warned against “any party, within or outside Lebanon, using Lebanon as a venue for proxy conflicts or in any manner contributing to instability in that country”.

On Friday, a spokesman for France's foreign ministry said: “We wish Saad Hariri to have all his freedom of movement and to be fully able to play the essential role that is his in Lebanon.”