On November 4, Hariri announced he was stepping down in a televised address from Riyadh, sparking rumours he was being detained against his will.
After French mediation, however, he rescinded his resignation the following month and was named premier for a third term this month after Lebanon's first parliamentary polls in nine years.
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"Hariri headed to Saudi Arabia for a visit expected to last a few days," his office said in a statement late Tuesday.
It is the premier's second visit to Saudi Arabia since his surprise resignation after an earlier trip in February.
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48-year-old Hariri, has started consultations to form a coalition government.
His Future Movement lost a third of its seats on May 6, when voters reinforced the strength of the Shia group Hezbollah and its allies.
Hariri has been prime minister since December 2016 and served his first term from 2009 to 2011.
Saudi Arabia has long been a key ally of Hariri, while Riyadh's regional foe Iran backs Hezbollah.
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