Beirut (AFP) - Four Russian cruise missiles aimed at targets in Syria crashed in Iran, a US official said Thursday, as regime troops backed by Lebanon's Hezbollah pressed a "vast offensive" against rebels in the war-torn country's west.The missiles were thought to be among a salvo fired Wednesday from Russian warships in the Caspian as part of a nine-day-old air war targeting foes of President Bashar al-Assad.Russia hit back at the claims, saying all the shots were on target, and the defence ministry posted a graphic on its website showing 26 missiles flying over Iran and Iraq before striking inside Syria.