Syrian forces were locked in fierce gunfights on Monday with rebels in one city and shelled another, as the UN chief urged “maximum restraint” after the arrival of observers to oversee a truce aimed at ending 13 months of bloodshed. An advance team of six international observers arrived in Damascus late on Sunday, the UN said. The delegation — the first of 30 monitors the UN Security Council approved on Saturday — will set up a headquarters and prepare routines to verify a cessation of hostilities. “They’ve arrived and they will start work (on Monday) morning,” UN peacekeeping spokesman Kieran Dwyer said.