A man reacts as he mourns the death of his relative after missiles were fired by Syrian government forces on a busy marketplace in the Douma neighborhood of Damascus.

The United States does not expect Saturday’s international talks to agree a plan to end Syria’s civil war, with participants divided over the fate of President Bashar al-Assad, Secretary of State John Kerry said.

But, he cautioned, enough common ground exists between the main protagonists Washington and Russia, Saudi Arabia and Iran to forge ahead with efforts “to develop a timetable for action based on interim steps.”

The Vienna talks, bringing together 17 countries and three international bodies, are the second round of negotiations between foreign actors with a stake in Syria’s four-and-a-half-year war.

The aim is to agree on a structure for a political transition and to decide which of the Syrian government, rebel and opposition factions — none of them yet represented at the talks — will take part.

At the first round last month, Kerry and his Russian counterpart Sergei Lavrov “agreed to disagree” about Assad’s role, allowing the talks to go forward but leaving their eventual success in doubt.

According to a leaked version of the latest draft Russian proposal, Moscow wants ally Assad to stay in office during an 18-month transitional period — a non-starter for Washington, which wants him gone.

“I cannot say this afternoon that we are on the threshold of a comprehensive agreement, no. There remains a lot of work to do,” Kerry said in a speech to the US Institute of Peace, before setting off for Europe.

“The walls of mistrust within Syria, within the region, and within the international community, are thick and they are high,” he warned.

“But those walls will never be breached unless we make a concerted and creative effort to surmount them. Our meeting at the end of October showed that the agreed basis for action is much wider than many had supposed.”

Kerry repeated the US view that Assad’s initial, bloody crackdown on pro-democracy protests had created room for the rise of the Islamic State of Iraq and Syria militant group, and that only his departure can unite Syrians.

In Vienna, Kerry will be joined by envoys from the Arab League, Britain, China, Egypt, the European Union, France, Germany, Iran, Iraq, Italy, Jordan, Lebanon, Oman, Qatar, Russia, Saudi Arabia, Turkey, the UAE and the United Nations.

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