The Assad regime is gaining ground as it takes advantage of infighting between Syrian opposition groups, in a sign of how the rise of extremists could tip the balance in the three-year-old civil war. Pro-regime forces have consolidated recent gains in and around the northern city of Aleppo, Syria’s economic hub. These forces are also geared up to recapture more territory around the city, in a potential major setback for rebels after 18 months of battles to oust the regime from parts of the city that have remained under its control. In one area, moderate rebels late last week succeeded in forcing extremists from Naqareen, northeast of the city. That withdrawal enabled pro-regime forces to move in against a weakened rebel contingent on Sunday. Pro-regime forces are also preparing for an assault on rebels in the nearby Sheikh Najjar area—a sprawling industrial district, said a resident and opposition activists. […]