The main Syrian opposition group has arrived in Geneva for peace talks
At least 60 people have died in a suicide bomb attack near a Shia shrine south of the Syrian capital Damascus.
Scores of people are also reported to have been injured in the bombings near Sayyida Zeinab.
The site has previously been targeted on a number of other occasions.
The blast comes as the country's main opposition group meets with Staffan de Mistura - the UN's peace envoy in Geneva.
Talks are to resume tomorrow with the head of the Army of Islam rebel group leading the opposition representatives.
The announcement has increased tensions between the two sides - but Mohammed Alloush has told AFP that he will be in Geneva by lunchtime on Monday.
Meanwhile, the High Negotiations Committee (HNC) says the peace talks with the Assad regime cannot get begin until there's an end to air raids on rebel territory.
They are also pressing urgent humanitarian aid for people in besieged towns across Syria.
Arriving in Geneva yesterday, the opposition group's spokesperson Salim al-Muslet said, "we're here to make this a success but must see change in Syria. Stop massacres. Save our children".
In a statement ahead of the talks, the HNC said they were at talks to 'participate, not negotiate'.
Ahead of the talks, UN envoy Staffan de Mistura has issued a message to the Syrian people, and said that the talks 'cannot fail'.
World powers have been intensifying their diplomatic efforts to solve the crisis in Syria.
They have pinned their hopes on an ambitious UN-backed plan for negotiations in Geneva, followed by the creation of a transitional government, a new constitution, and elections within 18 months.
Experts say there is a huge challenge ahead because the conflict involves moderate rebels, Islamist fighters, Kurds, and regime forces backed by Moscow and Iran.
Yesterday, Jane-Anne Mc Kenna, Director of Médecins Sans Frontières Ireland, said that residents of the besieged Syrian town of Madaya continue to die of starvation while the conflict continues.
She explains that MSF-supported medics have reported that 16 people have died in the town since the arrival of aid convoys earlier this month.
The conflict in Syria has resulted in the deaths of more than 260,000 people.