Iran''s Supreme Leader Ayatollah Ali Khamenei issued a religious decree to Muslims around the world on Sunday, ordering them to defend Palestinians against Israel''s attacks on Gaza, state television said.

"All Palestinian combatants and all the Islamic world''s pious people are obliged to defend the defenceless women, children and people in Gaza in any way possible. Whoever is killed in this legitimate defence is considered a martyr," state television quoted Khamenei as saying in a statement.

Israel launched air strikes on Gaza for a second day on Sunday and has killed more than 270 people in one of the bloodiest days in 60 years of conflict between the Palestinians and the Jewish state.

Israeli leaders said the campaign was a response to almost daily rocket and mortar fire by Gaza militants that intensified after Hamas, an Islamist group in charge of the coastal enclave Israel quit in 2005, ended a six-month cease-fire a week ago.

Iran refuses to recognise Israel, which accuses the Islamic state of supplying Hamas Islamists with weapons. Tehran denies the claim, saying it only provides moral support to the group.

Khamenei also criticised some Arab governments for their "encouraging silence" towards the Israel''s raids on Gaza.