The U.N. secretary-general instructed his special envoy to Syria on Thursday to relaunch a political process aimed at ending the four-year-old conflict, the clearest sign yet that a plan to freeze hostilities in key cities has failed.

Ban Ki-moon spoke to reporters Thursday about his new directive for Staffan de Mistura, the third U.N. envoy trying to end the conflict which has claimed more than 220,000 lives and driven some 9 million of the prewar population of 23 million from their homes.

The U.N. chief ordered de Mistura late last month to consult widely with U.N. Security Council members, regional governments and the Syrian parties themselves "to operationalize and flesh out" elements of the roadmap for a Syrian political transition adopted at a meeting on June 30, 2012 in Geneva by key nations.

The roadmap starts with the establishment of a transitional governing body vested with full executive powers and ends with elections — but there has been no agreement on how to implement it. It would require Syrian President Bashar Assad to relinquish power at some unspecified point.

But a senior U.N. diplomat this week said de Mistura is looking toward new political talks that build on meetings in Moscow, Cairo and elsewhere, not necessarily another round in Geneva.

De Mistura's predecessor Lakhdar Brahimi, who was the joint U.N.-Arab League mediator, led two rounds of peace talks with most of Syria's key players that ended in February 2014 without a breakthrough.

Since then, Russia, which staunchly backs the Assad government, has held another two rounds of peace talks, the latest this week in Moscow. They were boycotted by the leading Syrian opposition group but attended by a representative from de Mistura's office.

De Mistura, who was appointed by Ban last year, announced in late October that he was pursuing an "action plan" that involved freezing conflict in certain areas to allow for humanitarian aid and local steps of a political process toward wider peace. He wanted to start with Aleppo, but in early March the main opposition and rebel factions in the northern city rejected his proposal to freeze fighting in parts of the city, once Syria's largest.

The Swedish-Italian diplomat is expected to brief the U.N. Security Council on April 24, and the senior U.N. diplomat said he is expected to discuss his new "more top-down approach" to a political solution in Syria since "the bottom-up approach has run into the sand."

The diplomat, speaking on condition of anonymity because discussions on Syria have been private, said he didn't know whether de Mistura has given up entirely on the idea of local freezes, like in Aleppo, or has put it to aside to refocus on some form of political negotiations.

Russian Foreign Minister Sergey Lavrov urged the government and rebels to compromise to fend off the growing threat from Islamic extremist groups.