Syria's leading opposition figure Ahmad Moaz al-Khatib called on Wednesday in a letter addressed to Lebanon's Hezbollah chief Hassan Nasrallah to withdraw his fighters from Syria, and to help ensure the conflict does not spiral into a sectarian war.
"Hezbollah's intervention in Syria has complicated matters deeply, and I expected you, given your political and social stature, to play a more positive role" in the conflict raging in Syria, Khatib said in an open letter posted on Facebook.
"I ask you to withdraw Hezbollah's forces from all Syrian territory," added Khatib, in an address that was also filmed and posted on YouTube.
Syria's opposition and a monitoring group have accused powerful Lebanese Shiite movement Hezbollah of sending elite fighters into Syria, to support regime troops fighting insurgents.
Iran-backed Hezbollah is a close ally of President Bashar al-Assad's regime.
The accusations against Hezbollah have multiplied as fighting escalated this week in the Qusayr area near the Lebanon border.
Hezbollah has denied ordering its fighters to enter into Syria, but has claimed that Syrian rebels targeted Shiite areas of Syria inhabited by Lebanese.
It has said Shiites in Syria have a right to self-defence.
The majority of Syria's rebels, like the population, are Sunnis, while Assad belongs to the minority Alawite sect, an offshoot of Shiite Islam.
Khatib called on Nasrallah to "communicate with (Syria's) revolutionaries in the areas where the Shiite villages are located, to guarantee safety for all".
Three days on from his resignation as head of Syria's main opposition National Coalition, Khatib appealed to Nasrallah to help stop the conflict, which the UN says has left more than 70,000 people dead, from spiralling into a regional war pitting Sunnis against Shiites.
"The claim of defence for Shiite villages is unacceptable. Have the Shiites been in danger for the past several hundred years?" said Khatib, a moderate Sunni sheikh who has widespread support in Syria.
"There is a cunning plan to drag the Islamic world into sectarian conflict pitting Sunnis against Shiites, starting from Syria and Lebanon, only then to engulf all countries in the region, including Iran and Turkey," he warned.
Such a "crazy war would have no victor" and would "exhaust the finances of the Gulf countries", said Khatib.
He also reminded Nasrallah of how the Syrians in July 2006, during a 34-day war pitting Israel against Hezbollah, welcomed hundreds of thousands of Lebanese refugees fleeing the conflict.
"In the July war, we Syrians opened our houses and our hearts to the resistance (Hezbollah) despite our numerous ideological differences," said Khatib.
"Aren't 1,000 years of strife between Sunnis and Shiites enough for us to bury this narrow sectarian mentality?" he asked.