Russia and Saudi Arabia have failed in talks held in Moscow to overcome their differences on the fate of Syrian President Bashar al-Assad, a central dispute in Syria's civil war that shows no sign of abating despite renewed diplomacy.

Moscow has called for coordination between the Syrian government and members of an international coalition fighting the Islamic State of Iraq and the Levant (ISIL), which controls swaths of territory in Syria and Iraq.

Speaking after talks in Moscow on Tuesday, Saudi Foreign Minister Adel al-Jubeir reiterated Riyadh's stance that Assad must go.

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"A key reason behind the emergence of [ISIL] was the actions of Assad who directed his arms at his nation, not Islamic State [of Iraq and the Levant]," Jubeir told a news conference after talks with Russia's Foreign Minister Sergei Lavrov.

"Assad is part of the problem, not part of the solution to the Syrian crisis. There is no place for Assad in the future of Syria," he said.

Saudi Arabia is part of a US-led regional coalition conducting air strikes on ISIL positions in Syria and neighbouring Iraq, but Lavrov said this was not likely to successfully combat the group.

Talks with opposition

Jubeir and Lavrov said they discussed bringing various opposition groups closer together to improve their chances in facing ISIL and better coordinate in international talks on solving the conflict.

"The talks are about coordinating all those who are already fighting terrorists so that they put their main focus on fighting terrorism and leave for later settling scores between themselves," Lavrov said in describing Russia's proposal.

"More coordinated efforts on the ground would help reach the goal," he said, adding that this covered the Iraqi and Syrian armies, Kurdish forces and some armed Syrian opposition groups.

Lavrov said anti-ISIL forces united on the ground should have wide international backing. But Jubeir specifically ruled out any coalition with Assad and tension between the ministers was often visible during the conference.

Lavrov still said some "early details" have started to emerge under the Russian proposal but gave no further detail.

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He said Moscow would hold separate talks with Syrian opposition representatives including the Syrian National Coalition and Syrian Kurdish Democratic Union in coming days.

Moscow is looking to host another round of talks between Damascus and various Syrian opposition groups. Two rounds of such consultations have failed to yield any breakthroughs.

The two ministers also discussed possible Saudi purchases of Russian arms in the context of a planned visit by the Saudi king to Russia.