GENEVA — Syria’s opposing sides met face-to-face for the first time in U.N. mediation in three years Thursday, with the U.N. envoy citing a historic chance to end a conflict that has left hundreds of thousands dead, displaced millions and fomented a proxy war by foreign powers.

In a ceremony rich in symbolism, and as violent clashes continued in Syria, Staffan de Mistura convened government and opposition envoys for a new U.N. effort to cobble together a political process to halt suffering for millions of Syrians after nearly six years of war.

“The Syrian people all want an end to this conflict and you all know it,” he said in a cavernous U.N. assembly hall, addressing the warring sides. “They are waiting for a relief of their own suffering, and the dream of a new road out of this nightmare to a real and normal future in dignity.”

He took note of the presence of diplomats from the International Syria Support Group, which unites regional and world powers and is led by the United States and Russia. But Washington has been in political flux and de Mistura has said there’s uncertainty about the Syria strategy of the new Trump administration.

Earlier on Thursday, Russian President Vladimir Putin voiced hope for the success of a political settlement and said it would help defeat the “terrorist malaise.” U.N.-designated terrorist groups Islamic State and Fatah al-Sham, the al-Qaida branch in Syria, have been excluded from the talks.