Syria and its regional ally Iran are the main backers of the Lebanese opposition which has been at odds with the Saudi-backed Beirut government for months over the election of a new president.

"We haven't yet delivered invitations to Lebanon or to Saudi Arabia," a Syrian official told AFP, without giving an explanation.

Syrian Foreign Minister Walid Muallem handed an invitation to Qatari Emir Sheikh Hamad bin Khalifa al-Thani in Doha on Thursday to attend the March 29-30 summit.

The previous day he delivered an invitation in Abu Dhabi to United Arab Emirates President Sheikh Khalifa bin Zayed al-Nahayan.

It was unclear where the Syrian minister was headed next but Saudi media have made no mention of any planned visit.

The Arab League chief, who just left Lebanon after yet another abortive effort to broker a solution to the deadlock that has left the country without a president for the past three months, said some Arab countries were unwilling to attend the Damascus summit without a breakthrough.

"Some Arab leaders see the election of a president in Lebanon as a condition," Mussa told the Saudi-owned daily Al-Hayat.

"In other words, many of the leaders consider the election an essential element to the success of the summit," Mussa told the London-based newspaper.

Arab foreign ministers are to meet in Cairo on March 5-6 to prepare the summit, the League announced at its headquarters in the Egyptian capital.

Mussa said he would be visiting Damascus soon for talks on the summit, but he sided with the Beirut government against the opposition in insisting that it had executive powers amid the presidential vacuum.

The Lebanese constitution stipulates that in the absence of a president, the prime minister assumes his powers, but the Syrian-backed opposition insists Prime Minister Fuad Siniora's cabinet lost all legitimacy when six pro-opposition ministers quit in November 2006.

Mussa said the region was going through "one of the worst times for Arab relations" but insisted he had not lost hope of a resolution of the Lebanon crisis before next month's summit.

"It remains possible," he said.

"I had hoped that the last delay of the vote would not take place as there was no reason for it," he added, referring to the cancellation of a planned session of the Lebanese parliament on Monday to elect a president, the 15th such deferment since last September.

"Electing a president might have helped in resolving the remaining points of disagreement," he added, referring to opposition demands for a package deal also including an agreement on electoral reform and the make-up of a government of national unity to replace Siniora's administration.

The prime minister has received strong backing from the West in his standoff with the opposition.

Washington accuses Damascus and Tehran of trying to undermine the verdict of 2005 parliamentary elections in which Siniora's coalition won a majority.

But the opposition counters that Siniora has failed to respect the power-sharing arrangements in force since the 1975-1990 civil war, and Iran and Syria insist it is Saudi Arabia and the West, not them, who have been hampering a solution.