GENEVA - A week of U.N.-sponsored Syrian peace talks have been marked by strong differences between government and opposition delegates on what form a new constitution for the battered country should take.

Syria's warring factions have agreed that the agenda of their next meeting, set to begin January 25, would focus on basic principles to be included in a new constitution.

U.N. Special Envoy for Syria Geir Pedersen acknowledged that is not much, but it could be a door opener to a broader agreement.

He admitted discussions between the government and opposition delegations revealed many differences on positions and were marked by tense moments, but said none of that is surprising after 10 years of brutal conflict.

He noted the Syrian delegations listened respectfully to each other and were able to find common ground on some areas.

"There are some positions that they think we, hopefully, when we meet again it will be possible to build upon and that could create something that will be of importance when we actually, hopefully in the not-too-distant future, start to draft proposals for constitutional reform," he said.

The negotiations aim to draft a new constitution that will be a preamble to U.N.-supervised elections in Syria. Pedersen said the constitutional committee must make faster progress in resolving the thorny issue for the sake of millions of Syrians, who are deeply suffering from a protracted war.

"What is also important is to see that we see progress on the ground," he said. "That we make progress within the international community. That we encourage the new American administration and Russia, in particular, to sit down and to discuss to see if there are step-by-step, reciprocal steps that can be taken."

Doing that, he said, would help build the trust necessary to move forward on the stalled political process.

Syria's decade-long war has killed an estimated 400,000 people and displaced nearly 12 million people both inside the country and as refugees abroad.