BEIRUT, Lebanon — At least 31 Syrian troops, including four senior officers, were killed on Sunday in a bombing that collapsed a building on a government military base just north of Damascus, the Syrian capital, an antigovernment monitoring group said. It was one of the deadliest attacks on government soldiers in recent months. The deaths came as a government offensive against rebels continued on three fronts: in the outskirts of Damascus, in the south; outside Aleppo, in the north; and in the Qalamoun mountain region bordering Lebanon, in western Syria. The explosion, at the army’s transport base in the contested suburb of Harasta, appeared to have been set off by a device placed inside the building or in a tunnel, according to the Syrian Observatory for Human Rights , a Britain-based group that tracks the violence in Syria. The blast caused the building to collapse, the group said. There […]