Report: Thousands of Saudi, Chechen fighters in Syria's rebel ranks
According to the reports, some 14,000 militants from Chechnya have joined foreign-backed militant groups in Syria, making them the first in the ranking of the countries the Syrian militants originate from.
Some 3,671 Chechen militants have been killed in the conflict, while another 1,397 are missing.
Saudi Arabia was second in the ranking with 12,000 militants, the reports added.
Meanwhile, nearly 5,000 Palestinians, 4,000 Tunisians and 1000 Jordanians have joined the Al Qaeda-linked groups, al-Nusra Front and the Islamic State of Iraq and the Levant (ISIL), the reports indicated.
Syria has been gripped by deadly violence since March 2011.
Some sources say more than 130,000 people have been killed and millions displaced due to the violence between Western-backed rebels and the regime.