Antoine Ghanem, the Christian MP murdered in a Beirut car-bomb attack, was a member of the anti-Syrian March 14 block which forms the backbone of the Western-supported Lebanese Government. His death has reduced the number of seats held by the block in the 128-member parliament to 68 — only three more than the Opposition, led by the militant Shia Hezbollah.

Government figures have blamed Syria for Mr Ghanem’s murder, a charge denied strongly by Damascus.

Boutros Harb, a presidential candidate from the March 14 block, said “This is an attack aimed at sabotaging all efforts to reach a solution to the current political crisis. You cannot separate this killing from the presidential election.”

The block’s surviving MPs are scheduled to convene on Tuesday to elect a new president to replace Emile Lahoud, a close ally of Syria whose term ends on November 24. But security fears have complicated even further a gruelling political stalemate over the identity of the next head of state.

Some 40 MPs belonging to the March 14 block have sought refuge in a wing of the heavily guarded Phoenicia Hotel — one of Beirut’ s grandest, more accustomed to hosting millionaire holidaymakers from the Gulf states. Since the beginning of the year, Fouad Siniora, the Prime Minister, and most of his Cabinet have been working and sleeping in the Grand Serail, a hill-top Ottoman-era army barracks that houses the Government’s offices.

In Lebanon’s sectarian power-sharing system, the presidency is allocated to the Maronite Catholic community. Although several prominent Maronites have declared their candidacy, a consensus figure acceptable to both factions has yet to emerge, making it highly unlikely that a new president will be elected on Tuesday. The Lebanese Constitution demands that a president is elected by a two-thirds parliamentary quorum, which means that a successful poll will require agreement between March 14 and the Opposition.

Failure in the first round, however, means that a subsequent ballot can be held by a simple majority vote, which March 14 could win if the block is agreed on a candidate.

Lebanon has until November 23, the day before Mr Lahoud steps down, to elect a new president, and most analysts expect the crisis to continue until the last minute.

The Opposition has threatened to form a second, rival, government if the March 14 block elects one of their own — a move that would plunge the country into chaos and could spark civil strife.

Ban Ki Moon, the United Nations Secretary-General, has cautioned that the emergence of two governments would be the “worst case scenario” and has called for the timely election of a new president.

Efforts to resolve the crisis are complicated by the backing of Lebanese factions by regional and international powers. The March 14 block is supported by the United States and Arab allies such as Saudi Arabia and Egypt. The opposition is supported by Syria and Iran.

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