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

"The Geneva talks' next phase are crucially important because we will be focusing in particular on the political transition, on governance and constitutional principles," Staffan de Mistura told reporters after meeting 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 April 13, 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 which paved the way for the talks and called for elections in Syria to be held 18 months after a transitional government is agreed.

The fate of President Bashar al-Assad is a major sticking point, however.

While the opposition insists Assad can play no role in a future transitional government, the regime says voters should decide his fate.

According to state news agency SANA, Muallem confirmed 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.

Meanwhile, 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 group (IS) and Al-Qaeda's affiliate Al-Nusra Front are present.

De Mistura and Muallem also discussed humanitarian aid access to besieged areas, the envoy said.

The envoy also hailed the UN World Food Programme's "promising" first successful airdrop on Sunday on Deir Ezzor in eastern Syria, where 200,000 people live under IS group siege.