Two members of the Iran-backed Lebanese Shiite movement Hezbollah were killed on Wednesday in an Israeli airstrike in south-western Syria, a monitoring group reported.The Syrian Observatory for Human Rights said the attack also killed three paramilitaries fighting with troops of Syrian President Bashar al-Assad.The strike targeted the mainly Druze region of al-Hadr in the Quneitra province on the Golan Heights, the Britain-based watchdog added.Hezbollah broadcaster al-Manar reported that the attack had been carried out by a drone.An Israeli military spokeswoman declined to comment on the reports.Tensions between Hezbollah and Israel escalated following Israel's killing of a number of senior Hezbollah officials and Mohammad Allahbadi, a commander in Iran's Revolutionary Guards, in Syria's Golan Heights January 18.Hezbollah vowed to respond harshly and take their revenge. Iran also condemned and threatened Israel that accused Iran of provoking Hezbollah. A missile fired by the Lebanese Hezbollah group struck an Israeli military convoy on Wednesday. Israel, which reported unspecified casualties on the Israeli side, responded by firing at least 50 artillery shells into Lebanon in a significant escalation along the volatile border. The United Nations said a U.N. peacekeeper was killed in southern Lebanon, in an incident likely related to the border flare-up.