By Tom Perry and Tom Miles
BEIRUT/GENEVA (Reuters) - The Syrian opposition said on Wednesday there had been fewer breaches of a truce agreement by the government and its allies in the past day as a U.N. envoy unveiled plans to resume peace talks next week.
The "cessation of hostilities agreement" brokered by the United States and Russia has slowed the war considerably despite accusations of violations on all sides, preparing the ground for talks which the United Nations plans to convene in Geneva.
The talks will coincide with the fifth anniversary of a conflict that began with protests against President Bashar al-Assad before descending into a multi-sided war that has drawn in foreign governments and allowed the growth of Islamic State.
U.N. envoy Staffan de Mistura said he planned to launch substantive peace talks on Monday, focusing on issues of Syria's future governance, elections within 18 months, and a new constitution.
While the opposition High Negotiations Committee (HNC) has yet to declare whether it will attend, spokesman Salem al-Muslat said it was positive that the talks would "start ... with discussion of the matter of political transition".
He said the HNC would announce its decision very soon.
The Syrian government, its position strengthened by more than five months of Russian air strikes, has also yet to say whether it will attend. There was no immediate response from Damascus to de Mistura's remarks. The Syrian foreign minister is due to give a news conference on Saturday at noon (1000 GMT).
Peace talks convened in Geneva two years ago collapsed as the sides' were unable to agree an agenda: Damascus wanted a focus on fighting terrorism - the term it uses for the rebellion - while the opposition wanted talks on transitional government.
De Mistura aborted a previous attempt to hold talks on Feb. 3 and urged countries in the International Syria Support Group, led by the United States and Russia, to do more preparatory work.
The result was the cessation of hostilities which Western governments say has largely held since it came into effect on Feb. 27. It has been accompanied by more aid deliveries to opposition areas besieged by government forces, though fighting has continued in some important areas of northwestern Syria.
Rebel groups fighting to topple Assad had initially said they would support a two-week halt to the fighting. De Mistura said on Wednesday however that it was an "open-ended concept".
The next round of talks would not run beyond March 24. There would then be a break of a week or 10 days before resuming.
Asked if the talks could be delayed further from an original start date of March 7, de Mistura said the format gave him a lot of flexibility.
Jan Egeland, who chairs the Syria humanitarian task force, said the United Nations had delivered aid to 10 of 18 besieged areas across the country in the last four weeks, and was working to overcome obstacles and reach remaining areas.
The truce agreement, accepted by Assad's government and many of his enemies, was the first of its kind in a war that has killed more than 250,000 people and caused a major refugee crisis.
The agreement has not been directly signed by the warring parties and is less binding than a formal ceasefire. It does not cover Islamic State or the al Qaeda-linked Nusra Front, whose fighters are deployed in western Syria in close proximity to rebel groups that have agreed to cease fire.
Russia says it has recorded opposition violations including supplies of weapons via Turkey to rebels in Syria.
Muslat of the HNC said: "The violations of the truce were great at the start, but yesterday they were much fewer. There are perhaps some positive matters that we are seeing."
Speaking to Reuters, he said a government blockade of the Damascus suburb of Daraya must be lifted in order to "pave the way to the start of negotiations". He added this was not a condition for the attending talks but a humanitarian requirement.
Despite the relative success of the cessation of hostilities, the peace talks face great challenges, including the question of Assad's future.
The opposition says Assad must be removed from power at the start of a transition, while some of his Western enemies have backed away from that position, saying he must go at some point.
Russia has said that the matter should not be predetermined and Syrians should be left to choose. Assad has meanwhile ruled out anything that contravene the constitution, including the idea of a transitional governing body sought by the opposition.
Saudi Foreign Minister Adel al-JubeIr reiterated his government's tough line on Assad, who has also been boosted by Iranian military support. Saudi Arabia, which is in conflict with Iran across the region, has been a major sponsor of the Syrian insurgency.
"The choice for Bashar al-Assad is to either leave through a political process or the Syrian people will continue to fight until militarily they oust him," Jubeir said.
(Additional reporting by Lisa Barrington in Beirut and Stephanie Nebehay in Geneval; Writing by Tom Perry; Editing by Giles Elgood)