Saad Hariri, the Lebanese leader at the centre of a diplomatic row in the Middle East over his unexpected resignation as prime minister, has said he will return from Saudi Arabia in the coming days.

The announcement came in the form of a tweet on a day he met the visiting head of Lebanon's Maronite Christian Church in Riyadh, Patriarch Beshara al-Rai.

يا جماعة انا بألف خير وان شاء الله انا راجع هل يومين خلينا نروق ، وعيلتي قاعدة ببلدها المملكة العربية السعودية مملكة الخير . — Saad Hariri (@saadhariri) November 14, 2017

Lebanese officials have said Hariri, a Sunni Muslim politician and longtime ally of Saudi Arabia, is probably under either house arrest or in temporary detention in Riyadh.

Rai is the first Lebanese public figure to visit Saudi Arabia since Hariri announced his resignation in a televised speech from Riyadh more than a week ago.

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Dubai-based Al Arabiya TV quoted Rai as saying after the meeting in Riyadh that Hariri would return home as soon as possible.

Rai was also quoted as expressing his support for Hariri's reasons for resigning.

Besides Hariri, Rai held talks on the second day of his visit to the kingdom with the Saudi King, Salman bin Abdulaziz Al Saud, and the heir apparent, Mohammed bin Salman, at Al-Yamamah Palace in Riyadh.

The Saudi Press Agency SPA reported that the two sides "reviewed fraternal relations between the kingdom and Lebanon and discussed a number of issues pertaining to the role of different religions and cultures in promoting tolerance and renouncing violence and extremism".

Resignation speech

Reading out his resignation in a televised statement from Riyadh on November 4, Hariri blamed interference in Lebanon by Iran and its Lebanese ally Hezbollah for his decision, adding that he feared an assassination attempt.

His father, Rafik Hariri, was killed in a truck bomb blast in 2005.

Tuesday's developments came just days after Hariri rejected rumours he was being held in Saudi Arabia against his will and pledged to return to Lebanon "very soon" to affirm his decision to resign.

Speaking on Future TV, a station affiliated with his political party, the Future movement, Hariri said he was free in Saudi Arabia.

"Here in the kingdom of Saudi Arabia, I am free. I have complete freedom, but I want to look after my family as well," he said on Sunday.

"I'm not talking about months ... I'm only talking about days and I'll go back to Lebanon."

Hariri's resignation, just 11 months after he took office, has plunged Lebanon into uncertainty, threatening the country's fragile political stability and raising concerns over an open-ended crisis.

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

Hariri is part of a unity government that also includes rival political factions such as those supported by Hezbollah, a Shia group which is represented in the Lebanese parliament and has a powerful armed wing.

In a speech in Beirut on Friday. Hassan Nasrallah, the leader of Hezbollah, said Hariri was being detained in Saudi Arabia and that his "forced" resignation was unconstitutional because it was done "under pressure".

Nasrallah said he was sure Hariri was forced to resign as part of what he called Saudi Arabia's policy of stoking sectarian tensions in Lebanon.