Staffan de Mistura
Staffan de MisturaReuters

The UN peace envoy to Syria said Monday in Damascus that an upcoming round of negotiations in Geneva aimed at ending the country's five-year war would be "crucially important".

Staffan de Mistura's comments came as offensives by Syria's Al-Qaeda affiliate and allied rebels triggered a spike in violence that could endanger the negotiations.

"The Geneva talks' next phase is crucially important because we will be focusing in particular on the political transition, on governance and constitutional principles," de Mistura told reporters after meeting Syrian Foreign Minister Walid Muallem.

"We hope and plan to make them constructive and we plan to make them concrete," the envoy said.

Scheduled to resume on Wednesday, the Geneva talks are aimed at ending a conflict that has killed more than 270,000 people and forced millions to flee their homes since it erupted in March 2011.

The UN Security Council passed a resolution in December that paved the way for the talks and called for elections in Syria to be held 18 months after a transitional government is agreed.

Syrian President Bashar Al-Assad's fate remaining a major sticking point, with the opposition demanding he leave power – dead or alive – before any transitional government is agreed.

The regime says the president's future is not up for discussion.

According to state news agency SANA, Muallem confirmed on Monday the government delegation was ready for the next round of peace talks.

"Muallem reaffirmed in his meeting with de Mistura the Syrian position on the political solution to the crisis and the commitment to Syrian dialogue under Syrian leadership, without pre-conditions," the agency said.

De Mistura said he had also discussed with Muallem a shaky ceasefire in place since February 27.

"We did raise and discuss the importance of protecting and maintaining and supporting the cessation of hostilities which is fragile but is there, and we need to make sure that it continues to be sustained even when there are incidents to be contained," said the envoy, who spoke in English.

The truce, which was brokered by the United States and Russia, does not include areas where the Islamic State (ISIS) jihadist group and Al-Qaeda's affiliate Al-Nusra Front are present.

AFP contributed to this report.