The Russian Defense Ministry has claimed that the fighter that was downed in Syria's Idlib province was shot down by a man-portable air-defense system (MANPAD).
While the Syrian government has imported over 16,000 MANPAD systems from Russia and the Soviet Union between 1970 and 2010, according to the Stockholm International Peace Research Institute (SIPRI), many more have been supplied to opposition and militant fighters.
The United States was quick to deny any supply of MANPADS to opposition groups despite regular claims of US weapons supply made by different factions in the Syria.
Pentagon spokesman Eric Pahon told Russian media on Saturday, hours after the aircraft was downed by militants, that the United States did not equip partner forces in Syria with surface-to-air weapons.
"Alongside by, with, and through our partners in Syria, the United States remains focused on the fight against ISIS," he said.
"The US has not equipped any partner forces in Syria with surface-to-air weapons and has no intent to do so in the future. Our operations are geographically focused on ongoing combat operations against ISIS in eastern Syria. We will assess the validity of these claims to ensure the safety of our local partners. I refer you to the Russian government for information regarding this incident," Pahon said.
"MANPADS are available in the Levant from a number of different sources based on current deliveries as well as legacy systems which batteries no longer function," said Dr. Theodore Karasik, Senior Advisor, to Washington based think tank Gulf State Analytics.
"The Soviet Union, and later Russia, delivered MANPADS to the Syrian Army for air defense purposes. Turkey, through Rocketsan, also produces MANPADS for sale on the international market but delivered these weapons to many Syrian opposition forces, like the free Syrian Army, around Idlib, " he said.
According to Douglas Barrie, senior fellow for military aerospace at the International Institute of Strategic Studies, the SU-25 Frogfoot has been deployed in Syria by the Russian forces to provide close air support to ground troops.
"As such it was designed to be battle damage tolerant," Barrie told Al Arabiya English.
"At low-level the aircraft, irrespective of its ability to absorb some ground fire, remains vulnerable to attack," he added.
However if this loss, Barrie said, was due to only a single man-portable surface-to-air missile, it would have been of concern to the Russians.
"It would suggest a failure of the aircraft's defensive counter-measures to defeat an infrared guided missile on this occasion".
In Syria 19 groups have been proven to have acquired MANPAD systems according to researcher Eric Woods. In his published article Proliferation of MANPADS in Syria - Relevant Actors and Applicable Treaties for Policymakers, Woods identifies 19 groups half of which are supported by Turkey while the other half by the United States.
Video evidence shows that the majority of Turkish supported groups are utilizing FIM-92 Stingers.
The FIM-92 Stingers operate as an infrared homing surface-to-air missile. The system was developed in the US and entered service in 1981. The primary manufacturer is Raytheon Missile Systems but is also produced under license by EADS in Germany and by Roketsan in Turkey.
"As an example, it is known that the Free Syrian Army has acquired to enhance defense capabilities in Syria's north when FSA captured key airfields," said Theodore Karasik.
Also American MANPADS were delivered to the Syrian Democratic Forces, according to Karasik.
Other groups that video evidence proves their possession of MANPDS include Ahfad al-Rasoul Brigades, Bara bin Malik Battalion, Levant Front and Ahrar Al Sham.
"When combined with newer systems that have been delivered to Levantine combatants, the entire Levant may be awash in these dangerous weapons."
According to Maria Dubovikova, president of the Moscow based International Middle Eastern Studies Club, the timing of the attack is quite disturbing, as the Sochi congress in Syria has just passed.
"The Su-25 was targeted during his control flight around the de-escalation zone. De-escalation zones are considered the cornerstones of the peace process in Syria. The incident may pose one Russian retreat of forces from Syria," she said.
Dubovikova said that another possible source of MAPAD system might be the Ukrainians.
"It's difficult to prove, but they are always active on black market; especially after the rupture with Russia. There are some rumors here in Russia that it was an Igla MANPAD (9k38) SA18 or Chinese analogue FN-6 ".SHOW MORE