US allies said they had won assurances on Friday from new Secretary of State Rex Tillerson that Washington supports a political solution to the Syria conflict, ahead of UN peace talks.

On the sidelines of a G20 gathering in Germany, Tillerson joined representatives of several countries that support the Syrian opposition for talks on a way to end the nearly six-year war.

"All the participants want a political solution because a military solution alone won't lead to peace in Syria," German Foreign Minister Sigmar Gabriel told reporters in Bonn, adding that "Tillerson became very involved in the debates".

The meeting of the "like-minded" nations - made up of around a dozen Western and Arab countries as well as Turkey - was the first since President Donald Trump took office.

Diplomats said they were hoping for clarity on whether there has been a change in US policy on Syria, particularly on the future of President Bashar al-Assad.

The meeting came ahead of a new round of United Nations-led talks in Geneva on Feb 23 involving Syrian government and rebel representatives.

Under Trump's predecessor Barack Obama, Washington insisted Assad had to go, putting it at odds with Moscow which backs the Syrian government.

Trump has called for closer cooperation with Moscow in the fight against the Islamic State group, downplaying what happens to Assad as secondary to US interests.

With Russia's sway in the conflict growing, Moscow has seized the initiative by hosting separate peace talks in Kazakhstan along with Turkey, to broker a fragile six-week truce between Syria's warring parties.

Gabriel said the "like-minded" countries had agreed to step up pressure on Russia to back a political solution, reaffirming that there could be no alternative to the UN-led Geneva talks.

"Any political solution must be obtained in the framework of the Geneva negotiations and there should not be any parallel negotiations," he said.