Former prime minister Saad Hariri says supporting Aoun, an ally of Hezbollah, is necessary to protect the country.

Michel Aoun, a former military chief and ally of the armed Hezbollah group, is set to become Lebanon’s new president after receiving an endorsement from rival and former prime minister Saad Hariri.

Thursday’s endorsement paves the way for the 81-year old Maronite Christian leader to fill the post that has been vacant since May 2014.

“I announce today before you my decision to endorse the candidacy of General Michel Aoun for the presidency of the republic,” Hariri said.

He described his decision as necessary to “protect Lebanon, protect the [political] system, protect the state and protect the Lebanese people”.

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Hariri said the endorsement came after he had exhausted all other options and was intended “to preserve the political system, reinforce the state, relaunch the economy, and distance us from the Syrian crisis.

“We want to protect our country from this crisis,” he added.

For two years and five months, the Lebanese parliament has been unable to agree on a successor to former president Michel Suleiman.

Lebanon’s 128-member parliament is now expected to convene next week for a session to vote on the president – the 46th such session since Suleiman’s term expired in May 2014.

Lebanon’s president is reserved for a Christian candidate under a power-sharing agreement.

Lebanon’s 128-member parliament is expected to vote on Aoun’s nomination next week [EPA]

The endorsement comes as a surprise with speculation that it is the result of a deal that will allow Hariri to return as prime minister.

Al Jazeera’s Imtiaz Tyab, reporting from the capital Beirut, said Hariri’s endorsement of Aoun “raises some eyebrows” within Hariri’s Saudi and Western-backed Sunni-majority party.

He said at least two senior members of Hariri’s party announced they would oppose Aoun’s nomination.

“Hariri is finding himself in a very difficult position,” our correspondent added.

Aoun is allied with the Shia movement Hezbollah, which is backed by Iran and has dispatched fighters to neighbouring Syria to bolster the regime of President Bashar al-Assad.

He served as head of the armed forces and briefly as prime minister during Lebanon’s 1975-1990 civil war, when he was a staunch opponent of Syrian military presence in Lebanon.

But he shocked many by brokering an alliance with Damascus ally Hezbollah in 2006, a year after his return from exile in France and after Syria pulled its troops from Lebanon.

The current war in Syria has deepened existing divisions in Lebanon, with Hezbollah and its allies backing Assad’s regime, while Hariri and his partners support the uprising against him.

More than one million Syrian refugees have also sought shelter in Lebanon, straining the country’s already stretched resources and infrastructure.