Syria activists say Aleppo air raids killed 100

U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and more than two dozen other foreign ministers would gather for the Jan. 22 meeting at a Montreux hotel.

The conference will later reconvene on Jan. 24 for the start of actual negotiations between Syria's warring sides, said Khawla Mattar, a spokeswoman for the U.N.'s special envoy to Syria, Lakhdar Brahimi.

Violence in Syria has surged in the past weeks as the warring sides try to claim or hold on to territory as a possible bargaining chip in the negotiations.

The U.N. chief on Monday called for a cease-fire ahead of the peace conference, to give a chance for it to succeed, but the call fell on deaf ears.