Hayat Tahrir al-Sham (HTS) is a Sunni Islamist political and militant group that was set up in 2011 which has a key role in the Syrian civil war. The leader of the Islamist Group (IS) Abu Bakr al-Baghdadi was involved in the formation of HTS in 2011 under a different name, Jabhat al-Nusra.

In just a few days, a patchwork of forces has seized control of a broad stretch of land in the west and northwest of Syria.

Syrian rebel fighters are advancing southward after capturing much of Aleppo, Syria’s largest city, posing the most serious challenge to President Bashar al-Assad in years amid the country’s civil war,

Syrian government forces and their Russian allies are battling to hold back the offensive, with Russia launching airstrikes on Aleppo and the western city of Idlib on Sunday as Syrian government forces regroup, according to monitoring group The Syrian Observatory for Human Rights.

Assad’s regime seemingly came out of nowhere, and as Aleppo fell to Turkish-backed rebels in a matter of days, the Syrian president reportedly flew to Moscow.

National Security Adviser Jake Sullivan tells CNN’s Kasie Hunt that as of right now, the rebel offensive in Syria does not put US forces in the region at risk.