UN chief Ban Ki-Moon is holding bilateral talks with Syria's foreign minister Walid al-Moualem on the sidelines of major talks aimed at ending the conflict.
UN chief Ban Ki-Moon opened the Syria peace talks in Switzerland describing the occasion as a "day of fragile but real hope".
This is the first time delegates from both the Syrian government and opposition have been part of the same negotiations, but their openings speeches underlined the wide gap between their positions.
The UN Secretary General is "urgently considering his options" following the "disappointing conduct of some participants" in forthcoming peace talks on Syria, the Associated Press reports.
The report cites Ban Ki-Moon's spokesman as saying that he is "dismayed" after some participants threatened to pull out of the talks in protest at Iran's invitation.
The spokesman is cited as saying that the "disappointing public statement" made by an Iranian minister earlier today "fell short by some measure of what the Secretary General expected to hear".
UN Secretary General Ban Ki-Moon has said that "intensive and urgent" discussions are underway ahead of a major round of Syria peace talks on Wednesday.
Earlier, Iran's foreign minister Hosein Amirabdollahian is cited as saying that he would not accept any preconditions to take part in the 'Geneva 2' summit in Switzerland.
The ISNA news agency cited him is saying that it could not accept plans for a political transition in Syria as discussed at talks in 2012.
UN secretary-general Ban Ki-moon has invited Iran to day one of the Syria peace talks in Montreux, Switzerland, Reuters reported.
Chemical weapons have been used in the Syrian conflict, according to the final report by UN chemical weapons inspectors, which was presented to UN Secretary-General Ban Ki-moon yesterday.
According to the report, the weapons were used in a widely publicised attack in the Ghouta area of Damascus on August 21 and probably in four other locations - Khan al Assal, Jobar, Saraqeb and Ashrafiah Sahnaya - between March and late August.
The UN chief said: "The use of chemical weapons is a grave violation of international law, an affront to our shared humanity. We need to remain vigilant to ensure that these awful weapons are eliminated, not only in Syria, but everywhere."
The report did not determine whether the government or opposition were responsible for the alleged attacks. It will now be sent to members of the UN Security Council.
Ban Ki-Moon continues: "Mandela showed us the way with a heart larger than this stadium and an infectious smile".
"His long walk [is] complete," he adds.
UN Secretary General Ban Ki-Moon says that tens of thousands of people are gathered in "celebration of a mighty life".
He adds: "I hope we will be able to see the rainbow soon through the rain of sadness.
"South Africa has lost a hero. We have lost a father."
UN Secretary General Ban Ki-Moon has said that Syria's president Bashar al-Assad "has committed many crimes against humanity".
He added that he expects a report by UN weapons inspectors to confirm that chemical weapons were used in Syria.
The Secretary-General has accused the Security Council of suffering from an "embarrassing paralysis" on Syria and called on the international community to overcome the deadlock.
Ban Ki-Moon says he is considering asking the UN Security Council to demand Syria immediately transfer chemical weapons to safe sites where they can be destroyed.