The results of Sunday's election further bolster Iran's allies in Lebanon and neighboring Syria at a time when Tehran faces growing Israeli threats and the prospect of the United States pulling out of a landmark nuclear deal negotiated with world powers.
Hezbollah has gained political ground in Lebanon and consolidated Iran's influence on the fragile state's affairs after winning, along with its allies, a small majority in national elections.
FPM won 17 seats, a drop from 19 in the outgoing parliament that many analysts attribute to FPM's various alliances, especially lists where it ran with Hariri's Future Movement party, a match otherwise at odds with FPM's alignment with Hezbollah.
Under a system put in place when the civil war ended in 1990, the country's three most powerful positions are allocated along sectarian lines: a Maronite Christian holds the presidency, a Shia Muslim is the speaker of the parliament and a Sunni gets the prime ministership.
The most important achievement however was the one obtained by the Christian opposition party that is most critical towards Hezbollah, the Lebanese Forces of Samir GeaGea, which are expected to have nearly doubled their presence in Parliament from eight to 15 seats.
In a conciliatory tone, he congratulated all voters who participated in the elections and pledged to continue working with President Michel Aoun, who belongs to a rival bloc led by the militant Hezbollah.
"This is a great political and moral victory for the resistance option that protects the sovereignty of the country", Hassan Nasrallah said in a televised address.
According to Associated Press, Hariri lost five seats in Beirut where his party had a strong hold once.
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The strong showing by parties and politicians who support Hezbollah's possession of weapons risk complicating Western policy in Lebanon, which is banking on foreign aid and loans to revive its stagnant economy and receives US military support. Some 583 candidates stood for the 128-seat parliament, which is equally divided between Lebanon's Muslims and Christians.
"The Lebanese have had their say, and the word of our candidates was clear after our battle on different fronts", said Hariri.
FPM lost a few seats to Samir Geagea's Lebanese Forces (LF), which did notably well, almost doubling its number of seats from eight to 16.
Official results of the Lebanese election are expected on Monday.
This year's vote was according to a new election law providing for proportional representation for the first time.
On Sunday, many youngsters at polling stations said they hoped the election would mark the dawn of a new political era.
Separately, commenting on Twitter on Monday, Naftali Bennett, a hawkish member of the Israeli cabinet, said: "Hezbollah = Lebanon".
A better turnout than the 49.2 % introduced in a single day had been anticipated after the lengthy electoral hiatus however the brand new pre-printed ballots used Sunday appeared to confuse some voters.