A little over a week ago, Syria's embattled Assad regime used chemical arms against ISIS east of Damascus, despite the 2013 agreement to dismantle the regime’s chemical weapons. The regime apparently decided to use the lethal gas sarin after ISIS fighters attacked two Syrian air force bases considered vital military assets.

In 2013, Assad used chemical weapons against rebel groups several times. After more than a thousand civilians were killed in one case, the Obama administration declared that Syrian President Bashar Assad had crossed a red line. Washington threatened to attack in response but backtracked after reaching an agreement with Russia to dismantle Assad’s stores of chemical arms.

By early 2014, the weapons caches had been removed from Syria, and Western intelligence agencies believed that the Assad regime retained just a small amount of chemical arms for use if Assad’s rule were directly threatened. On a number of occasions, the regime used less-lethal chemical weapons like chlorine bombs.

Open gallery view A Syrian activist wears a gas mask in the Zamalka area, where chemical weapons were allegedly used in August 2013. Credit: Reuters

ISIS has also used chemical weapons in battle. Still, the regime’s return to using them is unusual and may be due to the importance it attached to this particular battle. It also may be due to Assad’s confidence since Russia began pouring in massive military aid last September.

With Russian backing, the Assad regime has been carrying out more conventional massacres as well. In the past week, hundreds of people were killed in the heavy bombing of Aleppo, including more than 50 people killed in a hospital run by Doctors Without Borders. Eyewitnesses said the hospital was deliberately hit in several rounds of bombing.

Damascus and Moscow denied involvement, despite the regime’s clear responsibility. For sure, the Russian air force recently took part in other airstrikes on Aleppo in which no effort was made to distinguish between military and civilian targets.

Israeli observers believe the regime is intent on driving out the last pockets of the city’s civilians. The Syrian army and related militias control the west of the city, while a diverse and flimsy coalition of rebel groups controls the east.

If Assad’s military campaign in Aleppo succeeds, it will strengthen the regime’s hold on northern Syria and help stabilize the areas under its control in the northwest, where the Alawites are concentrated around the cities of Latakia and Tartus.

Open gallery view Syrian men carry a body on a stretcher following a reported air strike on the rebel-held neighborhood of Al-Qatarji in the northern Syrian city of Aleppo, on April 29, 2016. Credit: Ameer Al-Halbi, AFP

A little more than two months after the declaration of a cease-fire, the renewed fierce fighting in Aleppo puts the partial lull in grave doubt. The United States is trying to calm things down and convince Russia and the Assad regime to halt the bombing of Aleppo. Due to the fighting in that city, many rebel groups are threatening to stop adhering to the cease-fire.

Syria isn’t the only front in the Middle East where Washington has been running into big problems. The fraught situation in Baghdad, where the government is embroiled in an internecine conflict with other Shi’ite forces, is threatening the Americans’ planned bid to lead a retaking of Mosul from ISIS.

Although the U.S.-led coalition has gained in its war on ISIS — by assassinating its leaders and hitting its oil reserves and funding sources — it's likely to face problems mobilizing the Iraqi army for an effective campaign in Mosul in the near future, especially given Baghdad’s fierce internal strife.