Riyadh (AFP) - President Bashar al-Assad can hold onto power in war-torn Syria only until a transitional council of opposition and government figures has been set up, the Saudi foreign minister said on Monday.

"We have said that... after the formation of the governing council Bashar al-Assad will have to leave," Adel al-Jubeir stated at a joint press conference with his German counterpart Frank-Walter Steinmeier.

The German minister was on a day-long stop in Saudi Arabia after visiting Iran seeking ways to end the war in Syria.

Germany has taken in 600,000 refugees from Syria and elsewhere since January as Europe grapples with its worst refugee crisis since World War II.

"Whether it's today, whether it's a week, whether it's a month, it's up to the Syrian people, but from the very beginning it's clear that Bashar al-Assad has no future in Syria", Jubeir said.

The governing council was proposed under a United Nations-sponsored Geneva 1 peace initiative in 2012.

The council would run state institutions and pave the way for elections.

Jubeir said the body can be formed while Assad is in office, "but once it's set up and running, there is no role for him".

Steinmeier, for his part, said that "in the long term there can be no solution there with Assad."

Saudi Arabia and other Gulf monarchies, as well as the West, support rebels in Syria.

Riyadh's regional rival Iran has sent military advisers and financial aid to help Assad, while Russia has launched air strikes in Syria targeting the Islamic State jihadist group and other "terrorists".

The United States and its allies say Russian warplanes are mainly hitting non-jihadist rebels battling Assad.

Resolving the conflict in Syria "has not become easier with the military involvement of Russia", Steinmeier said.

The IS group of Sunni extremists has seized large parts of Iraq and Syria where they have carried out widespread abuses.

Saudi Arabia and Germany are part of a US-led coalition which is taking on IS by aerial bombing and training or arming local forces on the ground.

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"We're not going to find the solution from the first steps. That's why combat against IS must continue while pursuing, in parallel, a process of political transformation in Syria," Germany's top diplomat said.

Four million people have fled the war in Syria since it began with anti-government protests in 2011.

More than a quarter of a million people have been killed, the Syrian Observatory for Human Rights monitoring group said on Friday.