The United Nations said yesterday it was gravely concerned about a flare-up of violence between Israel and Hezbollah, and called for restraint as the Lebanese Army said an Israeli plane violated its airspace. "The personal representative of the secretary-general for Lebanon Staffan de Mistura expressed his grave concern at the second serious incident involving violations of the Blue Line within the last eight days," a statement said. "(The United Nations) calls on all parties to exercise maximum restraint in order to achieve their stated intentions of maintaining calm." On Monday, Lebanon's Hezbollah resistance fighters detonated a bomb next to an Israeli bulldozer in the disputed Shebaa Farms border area, south of the UN-delineated Blue Line frontier. It was the second such attack in just over a week. According to the United Nations, the Israeli response lasted some three hours, including artillery fire and aerial bombs across the region that wounded two Lebanese civilian women. The last bout of violence on Jan. 9 — a Hezbollah attack on a vehicle in Shebaa Farms and subsequent Israeli strikes — killed an Israeli officer, a French UN observer and a Hezbollah fighter. The two incidents follow some six months of relative calm in southern Lebanon, which Israeli forces occupied for 22 years until 2000.