Iran's foreign ministry said attacks by its ally Hamas on Israel on Saturday were an act of self-defence by Palestinians, and called on Muslim countries to support their rights.

Palestinian Islamist group Hamas took Israel by surprise with the biggest attack in decades by gunmen who killed scores of people and brought hostages back into the Gaza Strip.

"This operation ... is the spontaneous movement of resistance groups and Palestine's oppressed people in defence of their inalienable rights and their natural reaction to the Zionists' warmongering and provocative policies," Iranian state media quoted ministry spokesperson Nasser Kanaani as saying.

"Iran considers that the Zionist occupier regime and its well-known supporters are responsible ... for the violence and killing against Palestinians and calls on Islamic countries to support ...the rights of the Palestinian people," Kanaani said.

Ali Akbar Velayati, a top adviser to Supreme Leader Ayatollah Khamenei, said in a statement: "This victorious operation will certainly expedite the collapse of the Zionist regime and promises its imminent annihilation," the semi-official news agency Fars reported.

Iran's Nournews, affiliated with a top security body, said the attacks "showed that, contrary to its claims of intelligence-security dominance over the resistance, Israel could not predict their operations, and that its Iron Dome was nothing but a dome of straw above a sand castle".

Government spokesperson Ali Bahadori-Jahromi told state media that the attacks "proved that the Zionist regime is more vulnerable than ever and that the initiative is in the hands of Palestinian youth".

Videos carried by state television showed people gathered at Tehran's Palestine Square to welcome the news of the attack, chanting "Death to Israel" and setting off fireworks. TV footage also showed scenes of jubilation in a number of cities across Iran.

Yahya Rahim Safavi, a former Revolutionary Guards commander who is now an adviser to Khamenei, earlier said: "We will stand by the Palestinian fighters until the liberation of Palestine and Jerusalem."

State television showed parliament members rising from their seats on Saturday to chant "Death to Israel" and "Palestine is victorious, Israel will be destroyed".