A second round of peace talks to end Syria's five-year civil war are due to resume in Geneva on Wednesday, as a surge in violence in northern Aleppo province threatened a fragile truce.
The United Nations-brokered talks are aimed at forming a transitional government followed by general elections to end a conflict that has killed more than 270,000 people and displaced half of the country's population.
The fate of President Bashar al-Assad remains a stumbling block, and UN Syria envoy Staffan de Mistura has held meetings with Assad's key allies Tehran and Moscow ahead of a sit-down with the main opposition High Negotiations Committee Wednesday and regime representatives later in the week.
A surge in violence in the last few days has threatened a landmark ceasefire agreed in February - which had largely held - and piled more pressure on these talks, which follow two previous fruitless attempts to negotiate an end to the bloodshed.