A Soviet-made Osa ("Wasp", NATO reporting name SA-8 Gecko) air defence system has downed an AH-64 Apache helicopter, according to a video published on Twitter - the authenticity of which cannot be confirmed.
The incident was allegedly filmed in November during a clash on the Arabian Peninsula.
The 9K33 Osa, created in 1970s, is a mobile surface-to-air missile system that can hit low-altitude targets at a range of 12 kilometres (7.5 miles). It is currently operated by numerous countries - predominantly in the ex-USSR, Asia, and Latin America.