Geneva: Talks on ending the war in Syria are expected to start on Friday and take six months, although invitations have still not been sent due to "intense disagreements", the UN Syria envoy Staffan de Mistura told a news conference on Monday.
"There are political risks. And you will hear them as soon as you will hear the fact that I intend to do them on the 29th and that we will be issuing invitations tomorrow," said De Mistura, who hopes to send out invitations on Tuesday.
Discussions on who should take part were ongoing in various capitals, including Washington, Moscow, Ankara and Riyadh, he said.
The first phase of talks would last 2-3 weeks, with a focus on a ceasefire, stopping IS and increasing humanitarian aid. Governance, a constitutional review and future UN sponsored elections would also be priorities, he said.
"I can tell you in advance, don't be surprised, there will be a lot of posturing, a lot of walk-outs or walk-ins because a bomb has fallen or because someone has done an attack, and you will see that happening. You should neither be depressed or impressed, but it's likely to happen.
"The important thing is that we keep the momentum."
The talks, often referred to as "Geneva 3" because of two previous UN processes that failed to stop the war, will also include women's groups, civil society and others, and De Mistura will begin with shuttle diplomacy between various camps, with "proximity" talks rather than face-to-face negotiations.
He will push for a countrywide "real ceasefire", including all parties except the two groups designed as "terrorists" by the United Nations - IS and Al Nusra.
Earlier in the day, US Secretary of State John Kerry said he hoped for "clarity" within 24 to 48 hours on Syrian peace talks that were supposed to have started in Geneva on Monday, and that it was better to delay a few days than to have them crumble at the start.
Kerry told reporters on a visit to Laos he agreed with the United Nations Special Envoy for Syria Staffan de Mistura that invitations for the talks should not be sent out until "you have pieces lined up."
The future of the talks was in the hands of the Syrian parties, he added.
"They have to be serious. If they are not serious, war will continue. Up to them - you can lead a horse to water; you can't make it drink," Kerry said.
"We have created a framework; the Syrians have the ability to decide the future of Syria.
"We will have to see what decision Staffan makes as to exactly how he is going to begin; but we don't want to decide and have it crumble on day one. It's worth taking a day or two, or three, or whatever.
He rejected comments from the lead negotiator of the Syrian opposition, who said on Sunday it was coming under pressure from him to attend the talks.
"I don't know where this is coming from. Maybe it's a pressure thing or an internal political thing, but that is not the situation," he said.
"They are the negotiators; so they will decide the future. What I did tell them is that it's by mutual consent. You have a veto, so does he, so you are going to have to decide how to move forward here," Kerry said, referring to Syrian leader Bashar Al Assad.
"The position of the United States is and hasn't changed, that we are still supporting the opposition politically, financially and militarily," he added.
Kerry said another meeting of the International Syria Support Group, of countries supporting the Syria peace process, had been "tentatively" called for Febraury 11.
Meanwhile, a suicide bomber driving a fuel tank blew himself up on Monday at a checkpoint run by Islamist group Ahrar Al Sham in Syria's northern city of Aleppo killing at least 23 people, a monitoring group said.
The Syrian Observatory for Human Rights also said that four of the group's commanders and four civilians are believed to be among those killed.
It said that the attack in the city's Sukari neighbourhood destroyed three nearby buildings and wounded dozens of people while many are believed to be stuck under rubble. Ahrar al-Sham officials were not immediately available for comment.