An alliance of Sunni Islamist militias in Syria that includes the al-Qaeda affiliate Jabhat al-Nusra have reportedly mounted a major offensive toward the country’s Alawite heartland in the home province of President Bashar al-Assad where many Christians reside.

News of the offensive comes as the as the top United Nations (UN) humanitarian official reported “grim statistics” about war in Syria, showing that some 220,000 people have been killed since the start of the conflict and 12.2 million others are in need of humanitarian assistance.

“The Army of Conquest, an alliance of Sunni Islamist militias that includes the al Qaeda affiliate Jabhat al-Nusra, announced the offensive via Twitter on Sunday,” reports VICE News.

According to a translation of the Sunni coalition’s statement by the Lebanese news website NOW, the group, which has already conquered much of Idlib province, pledged to “rain down a barrage of rockets and burning lava” on Assad’s native region, Qardaha, “so that Alawite villages can taste the evil that the Assad regime and Hezbollah’s hands have done.”

On Tuesday, the U.K.-based Syrian Observatory for Human Rights (SOHR) reported that the Sunni alliance has seized territory in the strategically important Sahl al-Ghab plain, an area located east of a mountain range that protects Qardaha and the Mediterranean coast from areas controlled by the rebels.

“Cities and villages along the coast are home to many Syrian Christians and members of Assad’s own sect, the Alawites, a Shiite group regarded as heretical by fundamentalist Sunnis,” notes VICE News. “These groups form the core of support for Assad’s regime, with many fearing persecution at the hands of the hard-line Sunni groups that now lead the resistance.”

A Syrian military source told Reuters that the offensive is both large and widespread.

“The Army of Conquest claimed on Twitter that they now hold several villages on the plain and around the city of Jisr al-Shughour to the north, as well as a nearby power station,” reports VICE News.

SOHR reported that the fighting continues, noting that two Jabhat al-Nusra-linked suicide bombers have detonated themselves in the area.

“The rebels say that their drive toward the Alawite heartland is vengeance for the regime’s assault on the town of Zabadani, which sits between the capital of Damascus and the Lebanese border,” points out VICE News.

Syrian government forces have hit the town with barrel bombs over the last three weeks while their Hezbollah allies moved in with ground forces, leading to what Stephen O’Brien, the UN under-secretary general for coordination of humanitarian affairs, described as an “unprecedented level of destruction and deaths among civilians.”

On Tuesday, O’Brien addressed the UN Security Council, saying that more than one million have been displaced in 2015 alone, bringing the total number of people removed form their homes to more than eight million, with an additional four million living as refugees in neighboring countries.

“There are no humanitarian solutions to this crisis. Each day that passes without the parties upholding their most basic obligations to protect civilians, and the strong demands of this Council, only results in more lives lost; more people displaced; more people without access to basic services; and a generation of children who struggle to obtain an education or have any sense of a future for themselves,” declared O’Brian.

“Syria today,” he reportedly added, “is the most acute, unrelenting and shameful blot on the world’s humanitarian conscience.”