"We have agreed on the Syrian National Pact. And we have agreed to continue our struggle together in unity to win our freedom and honor back," George Sabra, a member of the Syrian National Council (SNC), told a news conference after their two-day meeting in İstanbul late on Tuesday.
Leading opposition figures met in Istanbul on the invitation of Turkey and Qatar, current chair of the Arab League, to seek a common front in their year-old uprising against Assad.
Sabra said a transitional government will be formed after "the ousting of the existing government and regime," adding that a committee has been established to work to form a transitional government.
He said the committee would present its work on the formation of the transitional government to the referendum, which will allow the Syrian people to approve and pass freely.
Sabra added the İstanbul meeting embraced all groups within the Syrian opposition, noting that the participants of the meeting expressed support to the Free Syrian Army.
"The new Syria will be an independent and free country and a state equipped with necessary instruments "to decide on their own fate," he said.
Despite Sabra's messages of unity and solidarity, the meeting of Syrian opposition that aimed to show they can unite to form an alternative to Assad was marred when a veteran dissident and Kurdish delegates walked out, saying their views were not being heard.
Criticism of both the way the Syrian National Council, the main opposition umbrella group, was being run and the influence of the Muslim Brotherhood was rife among the more than 300 dissidents gathered at a seaside hotel in Pendik, a suburb on the Asian side of the Turkish city.
Speaking on the sidelines of a meeting dominated by the internal divisions, SNC spokeswoman Basma Kodmani voiced support for a peace and ceasefire plan drawn up by UN and Arab League special envoy Kofi Annan, so long as it led to Assad's removal.
"This is for us a position that cannot change because thousands of Syrians have died for it, Kodmani said.
The Syrian government said on Tuesday that it had accepted Annan's plan, but other SNC members dismissed Assad's word.
"He is buying time. It means more killing. He is playing games," said Adib Shishakly. "Every hour we are losing five people. So really, time is life."
In an opening address to the meeting, Turkish foreign ministry official Halit Cevik said there was no alternative to Assad's regime going, and he extended support to the SNC as a platform for different strands of the opposition.
Shortly afterwards, however, Haitham al-Maleh, a venerable opposition figure who was jailed by both Assad and his father, walked out of the hall after SNC President Burhan Ghalioun set out an action plan that called for greater unity.
"I want to see the council act democratically. Until now, they are acting like the (ruling) Baath Party," Maleh, who withdrew from the SNC last month, told Reuters.
Representatives of Syria's Kurds followed suit, saying the SNC had failed to explicitly address Kurdish hopes of having an autonomous federal region within a post-Assad Syria.
"If we don't reach an agreement now, these issues will be more complicated after the regime," Abdulhakim Basar, of the Kurdish National Council, told Reuters.
"Maybe we are afraid of an internal war between the Syrian factions, so we prefer to reach an agreement now to avoid this. Syria has to be for all Syrians without discrimination."
Opposition disunity has fed fears that Syria could slide into sectarian and ethnic conflict, giving pause to governments which would otherwise be glad to see Assad's downfall.
Turkey will host a "Friends of Syria" meeting of mostly Western and Arab foreign ministers on April 1 to try to agree measures to persuade Assad to call off his security forces, let in humanitarian aid and allow a political transition.
Leading opposition figures will also attend.
The splits among the opposition are unsurprising, given that political life in Syria has been dominated by 42 years of Assad family rule.
Fearful that the meeting could collapse, the Turkish hosts persuaded the SNC's executive to accept calls for change, according to signatories of an agreement approving the restructuring of the SNC and changes in its key personnel.
SNC chief Ghalioun, a Paris-based academic, said he would meet with all opposition blocs on Wednesday, after the official one-day conference is over.
Ghalioun had earlier outlined an SNC action plan that included raising international backing and support for peaceful protests. It also proposed that it should help organise and arm the rebel Syrian Free Army, established by army defectors to resist Assad's forces, and raise money to pay recruits.
Ghalioun also advocated the adoption of a "national oath", committing all the opposition to building a democratic state, without any agenda for revenge, and to seek reconciliation once Assad is removed.
"The executive council will have to do something to show it is listening to people," said a diplomat observing the meeting. "There is a feeling it is not transparent or democratic enough."
In Washington, US Secretary of State Hillary Clinton called on the Syrian opposition on Tuesday to show a clear commitment to include and protect the rights of all Syrians should a political transition occur.
Clinton also said Syrian President Bashar al-Assad, reported to have accepted former UN Secretary-General Kofi Annan's peace plan, would be judged by his actions and must order his forces to stop firing and to withdraw from populated areas.
Assad has been using the army to crush efforts to end his family's four decades of political dominance in Syria. Disunity among the opposition has accentuated fears that Syria could slide into sectarian and ethnic conflict, much as Iraq did after the 2003 U.S.-led invasion that toppled Saddam Hussein.
Speaking ahead of a gathering of Western and Arab nations in Istanbul to discuss a political transition in Syria, Clinton strongly pressed the Syrian opposition to lay out a vision of an inclusive Syria in which minority rights are respected.
"They must be able to clearly demonstrate a commitment to including all Syrians and protecting the rights of all Syrians," Clinton told reporters. "We are going to be pushing them very hard to present such a vision in Istanbul. So, we have a lot of work to do between now and Sunday."
She also reacted skeptically to reports that Assad has accepted Annan's peace plan.
"Given Assad's history of over-promising and under-delivering, that commitment must now be matched by immediate actions," she said. "We will judge Assad's sincerity and seriousness by what he does, not by what he says."
"If he is ready to bring this dark chapter in Syria's history to a close he can prove it by immediately ordering regime forces to stop firing and begin withdrawing from populated areas," she said, repeating previous U.S. demands for Assad to allow in humanitarian groups, to release political prisoners and to begin a process toward a democratic transition.