Moscow (AFP) - Russia said Wednesday that one of its fighter jets had approached a US-led coalition warplane in Syrian airspace for identification purposes, as it sought to allay US fears of mid-air collisions.

Russian warplanes including an Su-30SM fighter jet were bombing Islamic State group targets in Syria's Aleppo province when their warning systems "detected emissions from an unidentified flying object," defence ministry spokesman Igor Konashenkov said.

"Our fighter turned and flew to a distance of two to three kilometres (one to two miles from the plane), not with the aim of scaring someone, but to identify the object in question and to whom it belonged," he said in a statement.

Konashenkov said it was "not the first such case", adding that Russian pilots often come within visual recognition distance of US warplanes and drones.

Both Russia and a US-led coalition are bombing IS targets in Syria.

US Colonel Steven Warren, spokesman of the US-led coalition, had said earlier that the planes had come "miles apart" on Saturday, prompting fears that crowded skies over Syria could lead to mid-air collisions.

Warren said that all pilots had "conducted themselves appropriately" but that such proximity between aircraft was dangerous.

"But this is -- but it is dangerous, right?" he said at a briefing in Baghdad on Tuesday.

"It's dangerous if two sets of aircraft come into the same piece of airspace without very clear, laid-out protocols for safety of all involved, which is why we've sat down with the Russians to establish some safety protocols."

Moscow and Washington have been involved in talks on how to stay out of each other's way in the Syrian sky and Russian Foreign Minister Sergei Lavrov said on Wednesday that an agreement might be reached "any day now."

Russian and American defence officials are set to conduct a new round of talks via videolink on Wednesday.

Moscow launched a bombing campaign on September 30 in Syria, saying it needed to target Islamic State jihadists before they cross into Russia, which has a large Muslim population.

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However Washington and its allies have criticised Russia's intervention in the multi-front conflict, saying Moscow was also targeting Western-backed moderate rebels and seeking to prop up the regime of Bashar al-Assad.

"Russian combat aircraft are in Syrian airspace on completely legal grounds at the request of the official authorities of the Syrian Arab Republic," Konashenkov said.

"Moreover, all flights of our aircraft are coordinated with the relevant authorities of that country."