The Syrian government’s retaking of a town this weekend that had teetered beyond its control is sharpening sectarian tensions along one of the country’s most explosive fault lines: relations between the Sunni Muslim majority and the minority Alawite sect to which the family of President Bashar al-Assad belongs, residents and officials say…

One Sunni resident of Jisr al-Shoughour said he received a text message from an Alawite friend asking if his family was O.K. “I replied, ‘My two sisters with a baby have been killed,’ ” said the resident, who gave his name as Mohammed. Others accused Alawite neighbors of taking part in the crackdown, some coming from a town less than a mile away…

Alawites, on the other hand, shuddered at the prospect of Sunni insurgents who they believe may have helped wrestle Jisr al-Shoughour, at least momentarily, from government hands…

The prospect alarms outsiders as well, and has been one reason that the United States and Arab neighbors have as a whole been reluctant to push out President Assad. “The sectarian aspect, the divisions and the animosity are getting worse,” said an Obama administration official in Washington, speaking on the condition of anonymity.