The crisis in Syria is expected to dominate the two-day summit of the Arab League being held in Qatar.
Syria's opposition National Coalition has taken the country's official seat at the Arab League summit in Qatar.
Syria's opposition National Council has been invited to attend the summit in place of Damascus, which was suspended from the Arab League in November 2011.
The seat has been empty since the League suspended the government of Bashar al-Assad in November 2011.
The meeting comes at a time of disarray within the Syrian National Council (SNC) following the resignation of its head, Ahmed Moaz al-Khatib, on Sunday.
The two-day meeting in Doha comes at a time of disarray within the National Coalition following the resignation of its head, Ahmed Moaz al-Khatib, on Sunday.
Mr Khatib has said he still intends to address the summit.
Mr Khatib has said he still intends to address the summit.
After "consulting trustworthy figures", he had "decided to make a speech in the name of the Syrian people", he said on his Facebook page on Monday.
As the summit opened, the Emir of Qatar - president of the summit - invited the Syrian opposition to assume the official seat, the BBC's Jim Muir reports.
The decision to invite the SNC to the summit has enraged the government of Bashar al-Assad in Damascus.
Both Mr Khatib and the newly-elected interim Prime Minister Ghassan Hitto stepped forward and took the seat to the applause of the summit leaders, he adds.
The decision to invite the National Coalition to the summit has enraged Damascus.
"The League has handed Syria's stolen seat to bandits and thugs," Syria's official daily al-Thawra said.
"The League has handed Syria's stolen seat to bandits and thugs," Syria's official daily al-Thawra said.
But it is not yet clear whether the Arab League will simply hand the official Syrian seat to the opposition delegation, the BBC's Jim Muir reports from Beirut.
That is a step opposed by some Arab states, notably Iraq, Algeria and Lebanon, while others are concerned that it could set a legal precedent, he adds.
There will also be some concern at the current disarray within the official opposition.
Mr Khatib's resignation followed the decision by the SNC to elect, without consensus, an interim prime minister who has been outside the country for decades.
Some coalition leaders said the election of US-based Islamist Ghassan Hitto was "transparent" and "democratic", but it prompted several resignations from the SNC.
Mr Khatib did not give specific reasons for his resignation, but observers said he may have feared that Mr Hitto's election would further distance the outside opposition leadership from what is going on inside Syria.
Despite his resignation, there will still be a lot of interest in what Mr Khatib - seen as a respected and unifying figure in Syria - will have to say in Doha, our correspondent notes.
