GENEVA (Reuters) - The prospects for a new round of Syria peace talks should be clearer after the U.N. Security Council discusses options on June 29, U.N. Syria envoy Staffan de Mistura told reporters on Thursday.

De Mistura said he had accompanied U.N. Secretary-General Ban Ki-moon last week to St Petersburg, where they had "quite a comprehensive and long meeting" with Russian President Vladimir Putin and Foreign Minister Sergei Lavrov that mostly focused on Syria.

The last round of talks between the Syrian government and opposition broke up at the end of April as government forces, backed by Russia, escalated their assault on rebel-held areas in the northern city of Aleppo.

A "cessation of hostilities" that had brought peace to much of Syria for two months largely broke down, and the war has resumed in many areas.

De Mistura told reporters he was aiming for a July date for a new round of talks to meet an August deadline for a deal, but first he wanted the United States and Russia to make a "critical mass" of progress on a deal for political transition in Syria.

Despite the suspension of negotiations on a political transition - involving, crucially, the future of President Bashar al-Assad - officials have continued "technical" talks on some of the questions that need to be solved in any political deal.

De Mistura's team has held technical talks in Moscow and Cairo and plans more in Riyadh and Damascus, and he said so far they had been very useful.

"They are under the radar, calm and quiet and discreet but they have been providing us with quite a lot of substantive points that can be, will be useful, when the (next round of) intra-Syrian talks take place," he said.

De Mistura's humanitarian adviser Jan Egeland said the U.N. was still asking the government for permission to get into two besieged zones, Arbin and Zamalka in Rural Damascus. He hoped to reach the towns next week.

Egeland also warned that four towns covered by a single local peace deal - Zabadani, Foua, Kefraya and Madaya - had not had food deliveries since April. The humanitarian situation was in danger of sliding back to conditions at the start of the year, when people in Madaya were starving to death.

The agreement to get supplies into another besieged zone, the al-Waer suburb of Homs, was also "going badly", he said.

(Reporting by Tom Miles and Stephanie Nebehay; editing by Andrew Roche)