Sochi, May 12 (IANS/RIA Novosti): An international conference between representatives of both sides in the Syrian conflict is unlikely to take place before May end as earlier stated, as there are still too many differences of opinion over the event’s format.

A Russian source, who took part in Friday’s discussions in Sochi between Russian President Vladimir Putin and British Prime Minister David Cameron, has revealed.

“It is not likely to be possible before the end of May,” said the source. “It’s unrealistic to set any kind of rushed deadline.”

Russian Foreign Minister Sergei Lavrov said May 7 after negotiations with US Secretary of State John Kerry that the two countries had decided to hold an international conference at the end of May, aimed at facilitating a solution to the Syrian crisis through political dialogue.

The source present at Friday’s negotiations said that Putin and Cameron had discussed a range of possible concrete steps that could be taken to establish the format (of the event).

“There are a lot of conflicting opinions: who can participate in an event of that format, who is (a) legitimate (participant), and who is not,” he added.

“It’s obvious that this can’t be done without representatives of the opposition, but the question is, which opposition?” he said.

“We believe that there is no clearly defined center with whom negotiations could be held so that duties would then be carried out,” the representative of the Russian delegation said.

Syria has been locked in an increasingly bloody civil war since demonstrations broke out against President Bashar Assad in March 2011.

According to UN estimates, at least 70,000 people have been killed in the conflict.