At least two rockets fired from southern Lebanon hit open areas in northern Israel on Friday, and Israel returned fire, Israeli military officials said. No injuries were reported on either side. The Katyusha rockets were the first in six months to be fired at Israel from Lebanon. Israeli police said they had identified two sites where rockets fell near the northern town of Nahariya in the Western Galilee. It was not immediately clear who was responsible for the rocket fire. Hezbollah, a Shiite military and political organization in Lebanon, fired thousands of rockets at Israel during a 34-day war in 2006, but the group had assured the Lebanese government that it was not responsible for the previous attacks this year. Several small Palestinian and other militant groups operate in southern Lebanon and have fired rockets at Israel in the past. Rockets last struck northern Israel in late February, and before that in January, during Israel's three-week offensive against Hamas militants in Gaza to the south. Israeli military officials, speaking on condition of anonymity under army rules, said on Friday that they held the Lebanese government and army responsible for preventing such attacks. Israel did not give immediate details of the nature of its response, but news reports from Lebanon said Israel fired artillery shells at the source of the Katyusha fire, around the village of Al-Qlaileh near the southern Lebanese port city of Tyre. UNIFIL, the United Nations peacekeeping force in Lebanon, said in a statement on Friday that it was 'in contact with both sides, urging them to exercise maximum restraint, uphold the cessation of hostilities and avoid taking steps which would lead to further escalation.' The statement added that UNIFIL, in coordination with the Lebanese armed forces, had 'deployed additional troops and reaction forces in the area to prevent escalation.' The international peacekeeping mission helps Lebanese troops monitor the fragile truce that ended the 2006 war between Israel and Hezbollah. The Israel-Lebanon border has remained largely quiet but tense. 