The UN peace envoy to Syria said Monday that an upcoming round of negotiations in Geneva would be "crucially important" in finding a solution to the country’s brutal five-year war.

The UN peace envoy to Syria said Monday that an upcoming round of negotiations in Geneva would be "crucially important" in finding a solution to the country's brutal five-year war.

Staffan de Mistura's comments in Damascus came as offensives by Al-Qaeda affiliate and allied terrorists triggered a spike in violence that could endanger the negotiations due to resume Wednesday.

And the United States raised concern over the partial ceasefire that has largely held since February 27, alarmed by reports that national army is planning a major offensive to retake the city of Aleppo.

"We are very, very concerned about the recent increase in violence. And that includes actions we believe are in contravention to the cessation of hostilities," said State Department spokesman Mark Toner.

In Damascus, de Mistura said the next round of talks would be vital because they would focus on a political transition for Syria, where the fate of President Bashar al-Assad remains a major sticking point.

"We hope and plan to make (the talks) constructive and we plan to make them concrete," de Mistura told reporters after meeting Foreign Minister Walid Muallem.

The talks are aimed at ending a global war on Syria that has killed more than 270,000 people and forced millions to flee their homes since March 2011.

According to state news agency SANA, Muallem confirmed that the official delegation to the talks were ready for the next round of talks, while de Mistura said the pair had also discussed humanitarian aid to besieged areas.

De Mistura said he had also discussed the shaky ceasefire with Muallem.