HAMILTON, Canada The UN expressed grave concern Tuesday over ongoing hostilities in southern Lebanon, with the United Nations Under-Secretary-General for Peace Operations describing the situation as "appalling.” Noting that the United Nations Interim Force in Lebanon (UNIFIL) is currently operating under "very challenging and difficult conditions," Jean-Pierre Lacroix, speaking at a news conference, said "UNIFIL remains at all its positions and is carrying out a number of activities" to sustain