Story highlights The US says Syria attempted a similar bombing on Tuesday

Shootdown was first by US military of a manned aircraft since 1999

(CNN) CNN has learned new details of Sunday's rare air-to-air encounter between a Syrian Su-22 fighter and two US Navy F/A-18E Super Hornets in the skies over Syria, the first time a US warplane has downed a manned aircraft since 1999.

The incident took place after a series of clashes between pro-regime troops and the US-backed anti-ISIS group, the Syrian Democratic Forces, near the SDF-held town of Ja'Din, just south of Tabqah, Syria.

According to the Pentagon, the regime soldiers, equipped with tanks, artillery and technical vehicles, were advancing on the SDF position, forcing the coalition to use the de-confliction hotline with the Russians in attempt to turn the regime troops back.

When that proved unsuccessful, coalition aircraft performed "strafing runs" near the regime positions, which halted their advance.

Following that incident, coalition aircraft observed the Cold War-era Su-22 fighter fly over the SDF positions.

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