UN envoy to Syria Staffan de Mistura told the Security Council he sees slim chances for success in the latest round of talks next month to end the internecine conflict, diplomats said.

During closed discussions with the 15-member council yesterday, de Mistura acknowledged that the "odds and conditions for launching a political transition are no better now than six months ago" and the Damascus regime and opposition forces aren’t showing "much new willingness to negotiate" in the four-year war.

But "the UN remains convinced about the necessity to revive a political solution," he said, according to diplomats.

The mediator explained that he will hold separate consultations with the parties in May to probe the positions of the Syrian regime, the opposition and civil society groups, and see if they are ready for negotiations based on the Geneva statement.

The Geneva statement is a plan signed by major powers in June 2012 as a political settlement for the conflict following international discussions.

A UN spokesman said earlier that the new round of meetings would begin May 4. These consultations will last four to six weeks, said spokesman Ahmad Fawzi.

Iran, which was excluded from two international conferences on the conflict, has been invited, Fawzi said.

The latest efforts from de Mistura come after a failed initiative to negotiate local truces in the field, starting in Aleppo.