KABUL, Afghanistan—Reports of targeted killings in areas overrun by the Taliban mounted Friday, fueling fears that they will return Afghanistan to the repressive rule they imposed when they were last in power, even as they urged imams to push a message of unity at Friday’s prayers. Terrified that the new de facto rulers would commit such abuses and despairing for their country’s future, thousands have raced to Kabul’s airport and border crossings following the Taliban’s stunning blitz through Afghanistan. Others have taken to the streets to protest the takeover—acts of defiance that Taliban fighters have violently suppressed. The Taliban say they have become more moderate since they last ruled Afghanistan in the 1990s and have pledged to restore security and forgive those who fought them in the 20 years since a U.S.-led invasion. Ahead of Friday prayers, leaders urged imams to use sermons to appeal for unity and urge people not to …