By Maya Gebeily and Laila Bassam

BEIRUT (Reuters) -The powerful Hezbollah group and its allies thwarted a bid by their rivals to elect a top IMF official as Lebanon's president on Wednesday, sharpening sectarian tensions and further dimming prospects for preventing a collapse of the state.

Four years since Lebanon went into a financial meltdown that marks its worst crisis since the 1975-90 civil war, parliament failed for a 12th time to elect someone to fill the post reserved for a Maronite Christian under the country's sectarian system.

The standoff has opened a fresh sectarian fault line, pitting the Iran-backed, heavily armed Shi'ite Muslim Hezbollah against Christian factions including its own ally, Gebran Bassil, who endorsed IMF official Jihad Azour for president.

Neither Azour nor Hezbollah-backed candidate Suleiman Frangieh came close to winning the 86 votes needed to win in a first round vote. Azour, the IMF's Middle East Director and an ex-finance minister, won the support of 59 of 128 lawmakers.

Frangieh secured 51.

Hezbollah and its allies then withdrew from the session, denying the two-thirds quorum required for a second vote in which 65 votes are enough for victory.

Shi'ite Parliament Speaker Nabih Berri, a Hezbollah ally, did not schedule a new session. It leaves Lebanon with no immediate way of filling a post vacant since the term of the Hezbollah-allied President Michel Aoun ended in October.

Azour thanked lawmakers who backed him, saying he hoped the will expressed by "the majority of deputies" would be respected.

Hezbollah lawmaker Hussein al-Haj Hassan said the group was ready for dialogue but sticking by Frangieh, a friend of Syrian President Bashar al-Assad.

George Adwan, a Christian lawmaker with the anti-Hezbollah Lebanese Forces party, said the vote was "a major victory" because it showed Azour close to 65 votes.

But with parliament fractured, analysts say the logjam may now require the type of foreign intervention that has resolved past crises in Lebanon, including the 1989 deal mediated in Saudi Arabia that ended the civil war.

Lebanese political sources have anticipated that a new detente between Saudi Arabia and Iran could play out in Lebanon, but say they have not yet sensed pressure as other issues - including the Yemen war - take precedence.

A newly-appointed French envoy is expected in Beirut next week in a mediation effort.

Washington is concerned by the stalemate and wants to see a president elected who can unlock IMF support for Lebanon, but it is up to the country's leaders to resolve the crisis, U.S. State Department spokesperson Matthew Miller said.

"We believe that Lebanon’s leaders and their elites must stop putting their own interests and ambitions above the people of their country," Miller said at a press briefing.

SECTARIAN TENSIONS

"You can't stay in this situation," said Mohanad Hage Ali of the Carnegie Middle East Center, noting forthcoming state decisions included agreeing a replacement for central bank governor Riad Salameh, who faces corruption charges which he denies. His term ends in July.

Lebanon has been without a fully empowered cabinet since parliamentary elections last year.

Hezbollah, designated a terrorist group by the United States, unleashed fierce rhetoric against Azour, describing him as a candidate of confrontation.

Lebanon's Shi'ite Mufti Sheikh Ahmad Qabalan dialled up the attacks without naming Azour, accusing him of being backed by Israel and saying "a president with an American stamp will not be allowed".

Azour, 57, has said he wants national unity and reforms.

He was finance minister from 2005 to 2008, a period of political conflict pitting a government backed by the West and Saudi Arabia against Hezbollah-led opponents aligned with Damascus. That crisis culminated in conflict in 2008, with Hezbollah seizing much of Beirut.

The financial crisis was caused by decades of corruption and profligate spending by ruling politicians whose vested interests have obstructed any steps towards addressing it.

The cabinet passed a recovery roadmap in May 2022, despite objections by Hezbollah ministers. The IMF has criticised Lebanon for very slow progress in implementing reforms.

(Additional reporting by Issam Abdallah and Simon Lewis; writing by Tom Perry; editing by John Stonestreet, Mark Heinrich, William Maclean)