In this video we see the Muawiyah brigade launching one MILAN missile.
As you might know Liwa al-Haqq, Harakat Ahrar as-Sham and Jabhat al-Nusra captured eighty-eight MILAN missiles without launchers on the 15th of March 2013. These missiles were all of former Syrian Arab Army stocks, leftovers from the 4400 ordered in 1977 and delivered in 1978-1979. All the missiles delivered to Syria were of the F1 standard.
The missiles in the video are of the F2 standard. A variant, Syria is not known to have ordered. It is therefore simple to conclude the missiles seen in this video are being supplied from elsewhere.
The photo here below (taken from the video at 0:27) proofs the missile is of the F2 standard.
The direct supplier is either Libya or Qatar, both known operators of the missiles. Qatar even supplied the Free Libyan Army with some of her own MILAN missiles during the Libyan Revolution. Qatar owns the F2 variant, Libya owns the F3 variant(except the missiles given to Libya by Qatar which were of the F2 variant). This means the missiles are definitely coming from Qatar, either directly or via Libya.
Recent photos of the Libyan ship detained by Lebanese authorities in 2012 show MILAN F2 missiles in a shipping container. If a batch of those missiles did make it trough in recent times or the Free Syrian Army acquired the MILAN F2 missiles directly from Qatar remains unknown.
The major difference between the F1 and F2 variant can be seen here:
As you can see the penetration of the Milan F2 is way higher. Making it way deadlier against targets that need a high amount of penetration such as tanks.
Syria and her HJ-8s
Syria and her MILANs
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Syria and her AK-74Ms
Syria and her M99s