He also urged the international quartet - made up of the United Nations, European Union, Russia and the United States - to put pressure on Israel.
"This is not terrorism as Israel is claiming," Moussa said.
"The real problem is the Israeli military occupation. And, Israel as an occupying nation has a responsibility to protect the rights of the people of the occupied land."
The 57-member Organisation of the Islamic Conference supported the calls for an emergency meeting of the UN Security Council.
The criticism of Benita Ferrero Waldner, EU external relations commissioner, was also strong as she accused Israel of carrying out "collective punishment" of Gaza's 1.5 million people.
The EU commissioner warned that neither the closure of Gaza's border nor the deadly air raids and incursions of the past week would bring Israel security from rockets fired by Palestinian armed groups.
"Only a credible political agreement this year ... can turn Palestinians away from violence," she said.
Hosni Mubarak, the Egyptian president, phoned Ehud Olmert, the Israeli prime minister, on Monday to stress "the need to stop the Israeli aggression against the Palestinian people".
He also warned "of the deteriorating humanitarian situation resulting from the blockade imposed on the [Gaza] Strip by Israel."
The Hamas movement, which took full control of Gaza last June, has called on other nations to put pressure on Egypt to open its Rafah crossing with the territory to let in desperately needed supplies.
"We have one demand and that is the opening of the Rafah crossing and the breaking of the siege," Ismail Haniya, Hamas leader, said.
Peace talks 'a mockery'
Syria said Israel's actions made a mockery of the relaunched peace talks with the Palestinian government led by Mahmoud Abbas, the president.
"Talk of a peace process between Israel and the Palestinians flies in the face of the green light being given to the attacks and blockade," a foreign ministry statement said.
|Protesters took to the streets |
in many cities [AFP]
Neighbouring Lebanon called on Western powers to end their silence over Israel's military action against Gaza which has killed at least 37 people in the past week.
"Israel is profiting from the international silence ... to unleash its rage against the inhabitants of Gaza," Fuad Siniora, the Lebanese prime minister, said.