WASHINGTON — Following its recent capture of major cities in Syria, the Islamist militant group Hayat Tahrir al-Sham, or HTS, pledged to respect the rights of ethnic and religious minorities. Rights experts, noting the group’s extremist ideology and history of brutality, caution that these promises must be backed by tangible actions. HTS, a U.S.-designated terrorist organization, along with a coalition of Turkish-backed armed groups, has in the past week seized control of Aleppo, Hama and dozens of surrounding towns in northwest Syria amid a complete collapse of forces loyal to Syrian President Bashar al-Assad’s government. Shortly after capturing Aleppo, which