The west of Aleppo city has always stayed under control of the Syrian government. It inhabits about 1.5 million people. Over the last two weeks it has come into imminent danger of falling into Jihadi hands.
With large U.S. and Gulf supplies of new weapons, ammunition and intelligence some 10,000+ radical Jihadis, led by al-Qaeda in Syria, attacked Aleppo city. After several days they managed to break the south-eastern defense and created a small corridor into east-Aleppo. The area is besieged by government forces and under Jihadi control.
Aleppo as reported by "western" media
Several other large attacks followed but could barely be held back. The government forces are a mix of local defense units and auxiliaries from Afghanistan and Iraq. Their defenses seemed little prepared for the onslaught of suicide vehicles followed by mass infantry attacks. Moral was low and positions were given up without proper coordination.
The Syrian government and its allies could not use helicopters to support the defense as newly arrived MANPADs used by the Jihadis endanger any aircraft that flies low and slow.
To stop attacks and to prepare for counter moves valuable reserves had to be activated. Elite forces of the Lebanese Hizbullah and the Tiger brigade of the Syrian army were thrown into the battle. They managed to hold the Jihadi attacks for now but lack the mass to respond in kind.
The Russians have warned since April that such a large Jihadi offense was imminent, but it held back from any response while in talks with the U.S. administration. But the U.S. willingness to talk was largely a deception in support of the now ongoing attack.
The Jihadi campaign aims to occupy all of Aleppo city. It was named after a man who, in 1979, mass murdered a group of cadets belonging to a religious minorities. Should the Jidadis manage to win in Aleppo thousands of civilians will likely die. This would not only effect minorities. Aleppo is a Sunni city and the war is, contrary to "western" propaganda, not between religious minorities and the general Sunni population but between radical Sunni sects and their mainstream brethren.
About two weeks ago the Russian military openly prepared an appropriate response. Their most modern spy plane, a Tu 214R was send to Syria to collect targeting information. This in addition to two Il-20M reconnaissance planes already deployed there. Navy maneuvers along the Syrian coast as well as in the Caspian sea were prepared. Agreement with Iran about support measures were arranged.
At least seven Russian ships, all capable of launching Kalibr cruise missiles, were positioned in the east-Mediterranean and in the Caspian Sea. Yesterday long range Tu-22M3 strategic bombers and Su-34 tactical bombers deployed to Hamedan airbase in Iran. The route from Hamedan to Syria is 60% shorter than from Russia. The planes will thus be able to fly more often and with additional load. Iraq granted overflight rights. This open cooperation, publicly announced with pictures from the Iranian base, sends a loud message to the "international community" of Jihadi supporters. China adds to it by announcing tighter cooperation with the Syrian military.
Today a large scale bombing campaign against all support, supply and reserve assets of the Jihadis attacking Aleppo was launched. All major communications points, headquarters, depots and assembly areas between Aleppo and the Turkish border west of it will be bombed. Any reconnoitered fixed target will be attacked, probably multiple times, and destroyed. Then moving convoys and other targets of opportunity will come under attack. The campaign will continue for several days.
Such large scale attacks in the rear of attacking forces have no immediate influence on the front-lines. Expect some renewed Jihdai attacks on Aleppo city proper to divert from the slaughter of their assets in the rear. But after a few days their front-line supplies will run out and no new supplies will be there to arrive. The general attack on Aleppo will then falter.
All of this will only stall the situation in Syria. The Syrian government currently lacks the capability to retake and secure the large area between Aleppo, Idleb and the Turkish border. Additional changes in the strategic situation will be needed to turn the war into either direction.
But the then likely failed attack on Aleppo will have chewed up a large amount of assets and personal the U.S. supported Jihadis and their allies are able to deploy. The center of gravity of the war will probably move elsewhere, away from Aleppo proper.
All this of course depends on luck and all the other imponderables of war.