The Syrian National Coalition has rejected the resignation of Ahmed Moaz al-Khatib just hours after the former leader announced he was stepping down out of frustration.
In a statement released on his Facebook page on Sunday, Khatib confirmed his resignation from the dissident group recognised by dozens of states and organisations as a legitimate representative of the Syrian people.
"I announce my resignation from the National Coalition, so that I can work with a freedom that cannot possibly be had in an official institution," Khatib said in the statement.
"For the past two years, we have been slaughtered by an unprecedentedly vicious regime, while the world has looked on," Khatib said.
"All the destruction of Syria's infrastructure, the detention of tens of thousands of people, the forced flight of hundreds of thousands and other forms of suffering have been insufficient for the international community to take a decision to allow the people to defend themselves," he added.
His statement came hours after the Arab League extended an invitation to the opposition coalition to attend a summit in Qatar next week.
The pan-Arab bloc has suspended Assad's membership and recognised the coalition as the legitimate representative of the people of Syria where a two-year conflict has killed more than 70,000 people.
Khatib is a former imam and moderate Islamist who rose from independent ranks as a respected figure of dissent against the Damascus regime.
Sheikh Hamad bin Jassim Al Thani, the Qatari prime minister, said that he regretted Khatib's decision and urged him to reconsider.
Meanwhile, the armed Syrian opposition said on Sunday that it refused to acknowledge the authority of Ghassan Hitto, the coalition-appointed prime minister for rebel-held areas in Syria.
"We in the Free Syrian Army do not recognise Ghassan Hitto as prime minister because the National Coalition did not reach a consensus," at the March 18 vote, said FSA political and media coordinator Louay Muqdad.
"I speak on behalf of the [rebel] Military Councils and the Chief of Staff when I say that we cannot recognise a prime minister who was forced on the National Coalition, rather than chosen by consensus," Muqdad said.
Hitto won an election in Istanbul on March 19 after 35 out of 49 coalition members voted for him following some 14 hours of discussion in a closed meeting bringing together prominent opponents based both inside and out of Syria.
Several key coalition members, including official spokesman Walid al-Bunni, however, walked out of the meeting and boycotted the vote.
Later, at least 12 top coalition members announced they had suspended their membership of the opposition body in protest against an election result they viewed as illegitimate.
Meanwhile, opposition activists from Assad's Alawite Shia Muslim sect called for him to be overthrown, during a conference held in Cairo, the Egyptian capital, on Sunday.
"The Syrian regime is not an Alawite sectarian regime ... the Alawite sect was and is being held hostage by the regime,"
said the statement, which was read out by Alawite activist Tawfiq Dunia.
The group said that the only way out of the crisis was for Assad to step down.
"What is important is that all Syrians unite regardless of their sect," Samir Aita, a prominent economist and member of the Syrian Democratic Forum, told Reuters on the sidelines of the conference.
''We call on all Alawites inside Syria to support the Syrian revolution and sever their ties with the Syrian regime that has been using them against their brothers, claiming to the world that the regime is protecting the Alawite minority in Syria," said Ali Dayoub, a spokesperson for the Alawites Against Bashar al-Assad group.
"We want the Alawites to recognise these lies because an autocratic regime cannot protect anyone but itself."