"Although political measures taken by the regional countries are admirable, they are definitely not sufficient," Larijani said in remarks reported by the official IRNA news agency.
"It is expected of them that they send serious military aid to the Palestinians... why should Islamic countries not send weapons to Palestine?" he asked, saying Israel receives such aid from the US and Western countries.
Larijani also said regional states sending weapons to Syrian rebels should redirect that aid, without naming any countries.
Iran, a staunch ally of the Damascus regime, is also a key backer of Gaza's Hamas rulers and Israel's arch-foe.
Larijani's remarks came a day after Defence Minister Ahmad Vahidi encouraged Islamic nations to close ranks and retaliate against Israel's deadly attacks on the Gaza Strip.
The Jewish state launched a major air offensive on Gaza on Wednesday with a missile strike that killed the military commander of the Islamist movement Hamas which rules the territory.
Ali Akbar Velayati, the top foreign policy adviser to Iran's supreme leader, said on Saturday Israel's offensive showed "the dangers of this cancerous tumour's presence in the heart of Islamic lands."
He also accused US President Barack Obama of complicity in the attacks, IRNA reported.
"In the beginning of its new four-year term, the American administration is complicit in this major crime, and has added to its own war crimes record," Velayati said.