MOSCOW, April 13 (RIA Novosti) - Unidentified gunmen attacked an army patrol in eastern Lebanon, killing four soldiers and injuring at least 13 others, Lebanon's Naharnet news website reported on Monday.

The attack occurred on a highway near the town of Zahle in the Bekaa Valley, 30 km (19 miles) east of Beirut, when two mortars were launched at the patrol before they came under automatic weapon fire.

It is believed that the attack against the Lebanese army was in revenge for anti-drug raids, which the military has been conducting in the area.

During the Lebanese Civil War (1975-1990), the Bekaa Valley was the agricultural center for growing the opium poppy and marijuana, as well as a center for narcotics sales. The valley makes up 40% of Lebanon's arable land. After the war, the drug business in the Bekaa Valley was almost completely uprooted; however, it has begun to pick up steam again over the last few years.