GENEVA -- Members of the main Syrian opposition group said Monday they plan to give UN envoy Staffan de Mistura a "roadmap" for implementation of their humanitarian demands on Syria that they say must happen before they formally join indirect peace talks with a government delegation in Geneva.

Farah Atassi, a member of the opposition coalition known as the High Negotiations Committee, said the top priority should be to stop the "unprecedented bombardment by the Syrian regime" of rebel-held suburbs of the Syrian capital Damascus.

The group was to meet with De Mistura at UN offices in Geneva on Monday. But his spokeswoman, Khawla Mattar, said indirect talks between the two sides were unlikely before Tuesday. De Mistura rescheduled a planned meeting with the government delegation Monday morning because he wanted to hold an official meeting with the opposition before launching indirect talks.

The talks in Geneva are aimed at ending a five-year conflict that has killed 250,000 people and displaced millions, leaving vast swaths of the country in ruins. They have been slow in starting, largely because of disputes over which opposition groups can take part and opposition demands that the government allow aid into besieged rebel-held areas and halt its bombardments of civilians before the talks start.

"We have come to Geneva to seek relief for our people by insisting UN Security Council resolution 2254 is implemented, which means humanitarian relief, the lifting of sieges, and the end of attacks on civilians," spokesman Salem al-Mislet said in a statement.

The talks in Geneva are part of a process outlined in last month's UN resolution that envisions an 18-month timetable for a political transition in Syria, including the drafting of a new constitution and elections.

In Jordan, Britain's Foreign Secretary Philip Hammond said his country supports the peace talks, adding that "We expect both sides to participate in these talks in Geneva in good faith, and finally to provide the peace that the Syrian people deserve."

Hammond, who said Britain backs the moderate opposition, called for "complete and unfettered humanitarian access across Syria and an end to all violations of international humanitarian law, including the indiscriminate bombing of civilian populations."

As the Geneva talks sputtered, the violence on the ground continued with activists reporting a dramatic spike in Syrian and Russian attacks on rebel-held areas.

The Syrian Observatory for Human Rights reported an average of around 60 barrel bombs falling on the besieged rebel-held town of Moadamiyeh every day for the past three days. The town is located about 10 kilometres southwest of Damascus.

Ahmad Moadamani, an opposition media activist in the town, said helicopters dropped 10 barrel bombs in the span of few minutes on the southeast front of the town on Sunday evening.

He said 97 people, among them civilians, militants, and civil defence personnel, who arrived after the attack, suffered injuries.

"Most of them suffocated," he said. He said the pattern of injuries pointed to some sort of gas attack although he acknowledged they have no way of knowing for sure what it was.

Moadamani said residents in the town had no faith in the Geneva negotiations.

"We don't have any trust in the negotiations," he said. "When people are dying from the hunger or at the barrel of the gun, how are we going to pursue the Geneva negotiations?"

He described the humanitarian situation in the town as "terrible in every sense of the word," adding that conditions deteriorated after access to the town was choked off by the government on Dec. 26.

"We've lost most of our nutritional supplies," he said.

Moadamani said there were more than 1,500 cases of malnutrition in the town, including 50 severe cases of malnutrition among children.

"Until today, no food or humanitarian or medical aid is allowed into the city, and no humanitarian cases are allowed to leave," he added.

The opposition delegation said it will meet de Mistura Monday after receiving reassurances from several countries as well as the UN envoy regarding sieges on rebel-held areas and bombardment of civilians.

De Mistura has decided that these will be "proximity talks," rather than face-to-face sessions, meaning that he plans to keep the delegations in separate rooms and shuttle between them. He has tamped down expectations by saying he expects the talks to last for six months.

The UN human rights chief, Zeid Raad al-Hussein, meanwhile told reporters in Geneva he hopes that peace talks "will lead to the end of all these horrific abuses -- human rights abuses and violations of international humanitarian law -- that we are all too familiar with."

Al-Hussein added that the UN has a principled position that "no amnesties should be considered" for those suspected of having committed crimes against humanity or war crimes.

Associated Press writers Jamey Keaten and Bassam Hatoum in Geneva and Philip Issa and Zeina Karam in Beirut and Omar Akour in Amman, Jordan contributed to this report