The United States and Russia have reached a ceasefire deal in southwestern Syria, one of the combat zones in a six-year-old civil war, despite continued differences on the fate of Bashar Assad.

US Secretary of State Rex Tilerson said it showed the United States and Russia were able to work together in Syria and that they would continue to do so.

“We had a very lengthy discussion regarding other areas in Syria that we can continue to work together on to de-escalate the areas and the violence, once we defeat ISIS,” he said.

Tillerson said they would also “work together towards a political process that will secure the future of the Syrian people”.

But said that by and large the objectives of the United States and Russia in Syria “are exactly the same.”

But Washington and Moscow have long been at odds over Syria. The United States has often called for the removal of Assad.

Jordan’s Petra news agency said the ceasefire would go into effect as of Sunday.

Tillerson has said the United States was prepared to discuss joint efforts with Russia to stabilize Syria, including no-fly zones, ceasefire observers and coordinated deliveries of humanitarian assistance.

Tillerson was present at a meeting in Hamburg between US President Donald Trump and Russian President Vladimir Putin, along with Russian Foreign Minister Sergei Lavrov.

The United States and Russia held secret talks on creating a “de-escalation zone” in southern Syria, Western diplomats and regional officials said in early June.

The proposed zone was in Daraa province, on the border with Jordan, and Quneitra, which borders the Israeli-occupied Golan Heights, they said.

Syrian forces in recent months escalated their strikes in the southwestern city of Daraa in a campaign to reach the border with Jordan and wrest full control of the city.

They said on Monday they would suspend combat operations in southern Syria, but rebels said the military had violated the ceasefire by striking areas under their control.

Separately, Russia, Turkey and Iran failed in talks on Wednesday to finalize an agreement on creating four de-escalation zones in Syria after Ankara raised objections.

The failure was seen as a setback for Moscow, the main architect of the plan, as it seeks to take the lead in global efforts to settle the Syrian war. The United States is only an observer in the so-called Astana process.