On Tuesday, US and British media published new claims of Syrian government use of chemical weapons in the rebel-held northern city of Saraqeb, in Idlib province. The story, put forward by the antigovernment Idlib Civil Defense or “White Helmets” group, alleges that 30 civilians experienced breathing troubles after chlorine gas canisters were dropped from a helicopter in a residential part of the city. No deaths were reported.

The claim was first reported on the Idlib Civil Defence Facebook page. The group posted a YouTube video that purported to show area residents wearing oxygen masks.

Saraqeb is located in the same region that saw a Russian helicopter downed a day earlier, killing all five servicemen on board. Moscow strongly denied that any chemical weapon attack had taken place. In a statement, Kremlin representative Dmitry Peskov said that the Idlib Civil Defense claims were fabricated.

Meanwhile, Syrian government claims that rebel groups had killed five people in a chemical weapon attack on the government-held portion of Aleppo were virtually ignored by Western media. This deadly attack was verified by Aleppo’s health director, Mohamad Hazouri. “Five civilians were killed and eight others suffered suffocation due to a terrorist attack with shells containing poisonous gas,” he told the state-run news agency, SANA.

The Syrian Observatory for Human Rights reported yesterday that rebel shelling of government-held parts of Aleppo had killed 30 civilians since Monday, including women and children.

These facts were not reported in a lengthy Guardian article dedicated to the alleged government attack in Saraqeb. Other major US and British news sources, including BBC, Reuters, Fox and CBS, also focused their coverage on allegations of a government attack.

US State Department spokesman John Kirby acknowledged that Washington is “not in a position to confirm” the use of chemical weapons by the Syrian regime. Nonetheless, he threateningly added that if the allegations were confirmed, it would be “extremely serious.”

Allegations and insinuations that the Syrian regime is waging chemical warfare should be taken as a warning. In August and September, 2013, the Obama administration seized on claims of a Syrian government sarin gas attack—later proven by journalist Seymour Hersh and others to be fabricated—to bring the US to the brink of yet another full-scale war in the Middle East. Obama ultimately decided against direct US involvement after the British parliament scuttled UK entry, and amid mass popular disaffection with war and sharp divisions within the military-intelligence apparatus.

Obama’s last-minute pullback from direct US involvement has been the source of sharp recriminations in American ruling circles. Proponents of an attack, including the current Democratic presidential nominee, Hillary Clinton, viewed the decision as a humiliating retreat that would embolden Russia, which maintains its only foreign naval base in Syria.

The new claims come amid a rapid erosion in the position of the US-backed Islamist rebels in Syria. Government forces, backed by Russian air power, have made consistent gains over the past year, culminating in the current siege on the rebel-held city of Aleppo. Western portions of the city are already in government hands.

In an attempt to break the siege, rebel forces led by the Al Nusra Front—recently rebranded as Jabhat Fateh al-Sham (Front for the Conquest of Syria)—have launched a last-ditch offensive, attacking Aleppo on its southwestern outskirts.

The outcome remains unclear, though a Russian military spokesman, Sergey Rudskoy, claimed on Monday that the Islamist forces had been badly beaten. On Tuesday, rebel forces claimed that they had expanded their attack and that they had gained ground in certain Aleppo neighborhoods. This was disputed by Rami Abdel Rahman of the British-based Syrian Observatory for Human Rights, who stated that government forces had retaken five of the eight positions the rebels had gained on Sunday.

Iranian forces and the Lebanese Shiite movement Hezbollah are also reportedly involved in the fighting against Jabhat Fateh al-Sham.

“[T]his is really their last stand,” Middle East analyst Firas Maksad told Al Jazeera of the Islamist rebels. “If they lose Aleppo, which they’ve held a major portion of now for about four-odd years, they might as well have lost all the battle for Syria.”

The Islamists’ position is further threatened by the rapprochement between the Turkish government of President Recep Tayyip Erdogan and both Russia and Syria. Erdogan narrowly survived a US-backed coup on July 15, after he signaled his intention of normalizing relations with Damascus and Moscow.

Erdogan, who was reportedly alerted to the coup by Russian intelligence, has responded to US machinations by taking further steps toward cooperation with Russia. He will meet with Russian President Vladimir Putin in St. Petersburg on August 9 to discuss greater economic cooperation, including a proposed natural gas pipeline, dubbed Turkstream, that would bypass the US client state in Ukraine.

Turkey has been the main staging base for both Islamist fighters and weapons supplied by the US, Saudi Arabia and Qatar to fuel the fighting in Syria.

With its five-year-old war for regime change in Syria failing, the Obama administration is prepared to do almost anything to prevent defeat in a war that has already killed over 400,000, made upwards of 10 million into refugees, and destroyed what had been, prior to 2011, one of the most advanced Arab societies.

The US and its proxy fighters are clinging to sections of Aleppo, a city that had served as the major supply route for weapons distributed to Islamists across Syria—and where 250,000 people are believed to still reside. The US has sought to scuttle Russian proposals to evacuate the city through humanitarian corridors. US ambassador to the United Nations called the proposal “chilling,” and Secretary of State John Kerry has claimed that it is a “ruse.” For its part, Russia claims that Islamist militias are preventing residents from evacuating.

The US has opposed every serious effort at a negotiated settlement to the war, insisting that there can be no peace discussions without the removal of Bashar al-Assad. That is, Washington insists that the bloodletting must continue until regime change is achieved and Syria is reduced to a vassal state of the US.