The United Nations on Friday demanded swift investigations into fatal Israeli strikes across Lebanon to decide if they complied with international law."Lebanon is becoming a key flashpoint," UN rights chief Volker Turk told reporters in Geneva."I call for an immediate cessation of hostilities."Lebanon has been engulfed by the expanding Middle East war, after the Iran-backed group Hezbollah on Monday fired missiles at Israel to avenge the death of Iranian supreme leader Ali Khamenei.