Hotel Imperial, the site of international talks on Syria, is pictured in Vienna, Austria (Reuters)

Security staff stand in front of US Secretary of State John Kerry, center, left, and Russian Foreign Minister Sergey Lavrov, center right (AP)

UN Special Envoy for Syria Staffan de Mistura, left, US Secretary of State John Kerry, second left, and Russian Foreign Minister Sergey Lavrov, third right, meet with foreign ministers for talks on Syria at a hotel in Vienna (AP)

Egyptian Foreign Minister Sameh Shoukry, left, and German Foreign Minister Frank-Walter Steinmeier, second left (AP)

Chinese Vice Minister of Foreign Affairs Li Baodong, second left, and Iranian Foreign Minister Mohammad Javad Zarif, second right (AP)

Britain's Foreign Secretary Philip Hammond arrives in a hotel before a meeting in Vienna (Reuters)

U.S. Secretary of State John Kerry (L) talks to Russian Foreign Minister Sergey Lavrov (Reuters)

From left, Russian Foreign Minister Sergei Lavrov, Secretary of State John Kerry, Saudi Foreign Minister Adel al-Jubeir and Turkish Foreign Minister Feridun Sinirlioglu stand together (AP)

From left, Russian Foreign Minister Sergei Lavrov, Secretary of State John Kerry, Saudi Foreign Minister Adel al-Jubeir and Turkish Foreign Minister Feridun Sinirlioglu (AP)

Secretary of State John Kerry shakes hands with Staffan de Mistura, UN Special Envoy for Syria, before a meeting at in Vienna (AP)