In mid-October 2021, several Syrian opposition websites reported that the Iranian-backed militias stationed in eastern Syria had augmented their forces and positioned rocket launchers in the Al-Mayadin area, facing the territory controlled by forces of the Global Coalition to Defeat ISIS.
These reports were published several days after the Allies of Syria operations room –members of which include Iran, Hizbullah, and other Shi'ite militias – threatened to respond harshly to an attack which the Syrian regime claims was carried out by Israel, south of the city of Palmyra, on October 13, 2021.
The following are details from several reports published on Syrian opposition websites:
On October 15, 2021, the Syrian opposition website Euphratespost.net reported that according to "special sources," over the past two days Iranian-backed militias had transferred large numbers of military reinforcements to their positions on the banks of the Euphrates River which face the areas controlled by the Syrian Democratic Forces (SDF) and the forces of the Global Coalition to Defeat ISIS led by the U.S. The report states that members of the Al-Fatemiyoun militia, comprised mostly of Afghan Shi'ites, were sent to the city of Al-'Asharah as backup. The report further states that the militia positioned a new rocket launcher in the Al-Mazra'ah area, in the desert adjacent to the city of Al-Mayadin. At the same time, a local militia which answers to Iran, known as Tajammu' Al-Hadi, set up new military outposts in the village of Mahkan, opposite the town of Dhiban, which is under SDF control.
On October 17, the Eyeofeuphrates.com Syrian opposition website reported that militias loyal to Iran had "recently" positioned rocket launchers in the city of Al-Mayadin on the banks of the Euphrates River, which were pointed at the Al-Omar oilfield, where forces of the Global Coalition to Defeat ISIS are stationed. The reporter for the website managed to locate one such rocket launcher camouflaged among the ruins of a destroyed house near the 'Abd Al-Mun'im Riyad school. He wrote that the Islamic Revolutionary Guard Corps (IRGC) concealed several rocket launchers among the rubble of destroyed houses whose owners fled the city, and in some houses held by the Abu Al-Fadl Al-'Abbas militia. The reporter estimates that there are more than 15 such positions with about 35 rockets. The report also states that these positions are closely guarded by operatives and by surveillance cameras.
On October 18, 2021, the opposition website the Syrian Observatory for Human Rights reported that "in recent hours," trucks carrying the raw materials to make explosives arrived from Iraq at the positions of the Iranian-backed militias in the area of Al-Mazra'ah, in the desert adjacent to Al-Mayadin.
It should be noted that on October 16 the website reported that the Al-Nujaba movement had set up a factory for the production of shells, surface to surface rocket launchers, and various types of bullets. It is possible that that factory was the destination for the shipment of raw materials from Iraq which arrived on October 18. It is also noteworthy that on September 29, 2021, another Syrian opposition website reported that the Al-Fatemiyoun militia, which is also supported by Iran, established a workshop for the production of weapons so as to obviate the need for the weapons' convoys which travel from Iraq to Syria and are vulnerable to aerial attacks, presumably by Israel and the U.S.
 See MEMRI JTTM Report: Allies Of Syria Operations Room: The Response To The Attack On Our Positions In Palmyra Will Be Very Harsh; The Planes Flew Through Airspace Above Jordan And Al-Tanf, October 14, 2021.
 Euphratespost.net, October 15, 2021.
 Eyeofeuphrates.com, October 17, 2021.
 See MEMRI JTTM Report: Syrian Opposition Website: Pro-Iranian Shi'ite Militia Creates Ammunition Workshop In Eastern Syria, September 30, 2021.