A Syria monitor said Saturday that at least five ISIS members including a cell leader were killed in US strikes overnight in retaliation for an attack last weekend that left three Americans dead.Washington said a lone gunman from the ISIS group carried out the December 13 attack in Palmyra - home to UNESCO-listed ancient ruins and once controlled by extremist fighters - that killed two US soldiers and a US civilian.For all the latest headlines, follow our Google News channel online or via the app.In response, the United States “struck more than 70 targets at multiple locations across central Syria with fighter jets, attack helicopters and artillery,” US Central Command (CENTCOM) said in a statement.Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP that “at least five members of the Islamic State group were killed” in eastern Syria’s Deir Ezzor province, including the leader of a cell responsible for drones in the area.A Syrian security source told AFP that