The Wall Street Journal reports: Several high-ranking Syrian military officials joined the opposition to President Bashar al-Assad on Thursday and Friday, in the Syrian conflict’s biggest wave of military defections to date.

The defections appeared to boost Syria’s armed opposition, and exposed corrosive sectarian splits in Syria’s army, between a largely Sunni core of soldiers and the highest officials, many of whom are from the same minority Alawite sect as President Assad.

The defections also appeared to lay the ground for new struggles within Syria’s already-fractured opposition. The rebel Free Syrian Army, led by a former Syrian army colonel since its founding last year, has since been joined by higher-ranking officers. A brigadier-general who defected in January is preparing to split into his own armed group, rebels familiar with his plans said Friday.

U.S. intelligence officials said that while the opposition movement is fractured—they cited 32 constituent groups from around Syria, including Islamist, Kurdish and secular groups—the armed rebels appear to be gaining momentum against the regime. The rebels are likely to win out eventually, these officials said, but are up against a more powerful military than insurgents faced in Libya.