Government supporters plan to mark Hariri’s killing in same Beirut square occupied by opposition protesters.

Lebanon's feuding pro- and anti-Syrian factions are headed for a standoff Wednesday after government supporters announced plans to mark a key anniversary in the same Beirut square where the opposition has been holding a sit-in for more than two months.

Anti-Syrian parties in the governing coalition called on their backers to turn out in huge numbers to commemorate the February 14, 2005 murder of five-time premier Rafiq Hariri that helped force the withdrawal of Syrian troops and brought Damascus foes to power.

They called on supporters to gather in the central Beirut square where an estimated one million turned out on March 14, 2005, but where hundreds of opposition activists have been protesting round-the-clock since late last year.

"We call on the Lebanese who loved Rafiq Hariri to commemorate the second anniversary with a massive gathering in Martyrs' Square in downtown Beirut," said a statement from the March 14 coalition, which takes its name from the 2005 rally.

The opposition is demanding that the rump anti-Syrian cabinet left after the departure of six pro-Syrian ministers last November make way for a government of national unity and fresh elections.

Its supporters have been camped out in the northern part of Martyrs' Square and the adjacent Riad Solh Square in an open-ended protest since December 1.

Security forces recently erected a fence slicing Martyrs' Square in half, in an apparent bid to prevent friction between pro-government supporters and those of the Syrian-backed opposition.

Two weeks ago, street fighting between opposition and pro-government supporters in Beirut and elsewhere left seven people dead and 300 wounded.

The opposition sit-in is spearheaded by Shiite militant group Hezbollah for which Wednesday is also a key milestone, marking six months since a devastating 34-day war with Israel ended in a UN-brokered ceasefire that allowed it to claim a score-draw.

Hariri's widow wrote to Hezbollah leader Nassan Nasrallah to appeal for national unity on the anniversary of her late husband's death.

"I appeal to you for us all to gather around his grave to make of this sad day a demonstration of love and unity ... and to give back to Lebanese the hope of a better future," Nazek Hariri wrote in the letter published in the Beirut press Sunday.

The anti-Syrian cabinet has declared Wednesday a day of national mourning.

"Public institutions will take a day off work on Wednesday, February 14 on the second anniversary of the martyrdom of Rafiq Hariri and his companions," a government decree said.

The Arab League has been attempting to mediate in the crisis which threatens to paralyse all government decision-making as Lebanon endeavours to repair its shattered economy after last summer's conflict with Israel.

But most eyes have been on regional rivals Iran and Saudi Arabia, key backers of Hezbollah and the government respectively.

"I think it's possible to find a solution by looking to the Iranians and Saudis," said Ali Hassan Khalil Khalil, an MP with the opposition Amal party whose leader Nabih Berri has an effective veto over all legislation as speaker of parliament.

Analyst Ahmed Baydoun said he doubted rival Lebanese leaders could agree a long-term political settlement but said he thought Riyadh and Tehran might broker a short-term deal.

Shiite-ruled Iran and Sunni-ruled Saudi Arabia "do not want to see Sunni-Shiite conflict like that gripping Iraq take hold in the entire region," he said.

But pro-government MP Samir Franjieh warned that the opposition of Iran's regional ally Syria to the formation of an international tribunal to try suspects in Hariri's killing would torpedo any deal.

"Any agreement between Saudi Arabia and Iran on calming Lebanon is going to run up against the hostility of Damascus, Tehran's ally, which is opposed to the court's creation," Franjieh said.

Hariri was killed along with 22 others in a massive bombing on the Beirut seafront widely blamed on Syrian officials and their Lebanese allies. Damascus has repeatedly denied any involvement.