MASNAA BORDER CROSSING, Lebanon — Powerful new explosions rocked Beirut’s southern suburbs late Saturday as Israel expanded its bombardment in Lebanon, also striking a Palestinian refugee camp deep in the north for the first time as it targeted both Hezbollah and Hamas fighters. Thousands of people in Lebanon, including Palestinian refugees, continued to flee the widening conflict in the region, while rallies were held around the world marking the approaching anniversary of the start of the war in Gaza. The strong explosions began near midnight after Israel’s military urged residents to evacuate areas in Dahiyeh, the predominantly Shiite collection of suburbs on Beirut’s southern edge.