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BONN, Germany (Reuters) - Countries opposed to Syrian President Bashar al-Assad will meet on Friday for the first time since Donald Trump’s U.S. administration took office, to seek common ground ahead of U.N.-backed peace talks in Geneva next week.

The talks on the sidelines of a G20 foreign ministers meeting come as Assad, backed by Russia and Iran, is in his strongest position since the early days of the civil war, and as Trump’s policy on Syria remains unclear.

“It’s urgent to meet to see whether all the like-minded countries are on the same page,” said a senior French diplomatic source. “It’s a chance to get everyone pushing in the same direction before the Geneva talks.”

He said the meeting between the United States, France, Britain, Turkey and Saudi Arabia and others would be the first opportunity to “test” U.S. Secretary of State Rex Tillerson’s position on Syria and how that fitted into the new administration’s thinking on defeating Islamist militants.

A second European diplomat said it was unclear to what extent Tillerson represented the views of Trump himself.

“On the fight against Islamic State, we’re comforted, but the question remains what will be the relationship with Russia? The Americans will gradually realize that everything is linked and that the fight against Islamic State and an alliance with Moscow also implies choices in the region and a long-term vision,” the first source said.

“You can’t just do a grand deal with Moscow and hope things will be resolved.”

Turkey, which has been a major supporter of the rebellion against Assad, has, with Russia and Iran, brokered a shaky ceasefire.

“It’s also urgent that we see where Turkey stands in light of the newfound proximity with Russia and Iran,” the source said, adding that it would be vital to assess how Gulf Arab Sunni states Saudi Arabia and Qatar - opposed to Assad - saw the conflict after “pulling back a little”.