In a speech marking the Muslim celebration of Eid al-Fitr, Ayatollah Khamenei said Israel was acting like a "rabid dog" and "a wild wolf" in acts that are causing a human catastrophe and which must be resisted.
"A people surrounded in a small place with closed borders, unsure of having water and electricity, this population faces an armed enemy," he said of three weeks of offensive in the Gaza Strip that has killed more than 1,100 Palestinians and 53 Israelis.
"The people resist unabated. This is a lesson for all."
Ayatollah Khamenei dismissed talk of a ceasefire in Gaza, saying it was a ploy by the United States and European states to save Israel and said Hamas should be re-armed, rather than disarmed as otherwise they will be "unable to defend themselves".
"The US president issued a fatwa that the resistance is disarmed so that they cannot respond to all those crimes (committed by Israel)," the leader said, referring to a call by Barack Obama for the "disarmament of terrorist groups and the demilitarization of Gaza".
"We say the opposite. The world and especially the Islamic world should arm ... the Palestinian people," the Leader said.
The Leader’s comments follow rallies held across Iran on Friday in a show of support for Palestinians and to protest against Israeli military action in Gaza.
On Thursday, the speaker of Iran's parliament, Ali Larijani, told Al-Alam news channels that Tehran had provided Hamas with the technology it has used to rain down rockets on Israel.
During the last major conflict in and around Gaza in November 2012, Larijani said Iran was proud to have provided "both financial and military support" to Hamas.
BA/BA