UNITED NATIONS - UN Special Envoy for Syria Staffan de Mistura said here Wednesday that while this month's planned opposition talks have been postponed until July, August is still the target for a political transition for the beleaguered nation.

"I have not indicated a fixed date in July because we want to make sure consultations among (opposition) co-chairs has sufficient critical mass so that when we call the talks there is a possibility of moving forward and political transition by August is still an option," he told reporters after briefing members of the UN Security Council.

De Mistura said he was aiming for talks among the splintered opposition fighting in the Syrian civil war "within July but not at any cost and not without some guarantees ... as a period where we should be seeing something concrete so that in September we take stock."

Late September is the annual gathering of world leaders at UN Headquarters in New York.

The fighting in Syria is now in its sixth year with a toll of more than 400,000 lives and the displacement of millions of people.

When asked if August wasn't "unrealistic" in getting to political transition, he reminded that the cessation of hostilities earlier this year appeared unrealistic but held for the greatest part of two of the following four months.

"While we are talking about the talks, there is a lot of discreet diplomacy which is taking place while we are talking," de Mistura said. "I've been to St. Petersburg (in Russia), I'm going to Washington tomorrow (Thursday). We consulted with the Security Council (Wednesday). So let's see about it in August."