Amnesty International called on the UN Security Council to condemn the Israeli military offensive in Gaza and take action to ease the humanitarian situation there.
Malcolm Smart, director of the Middle East and North Africa programme at the London-based rights organisation, said: "Civilian casualties and destruction in Gaza are on an unprecedented scale.
"The UN Security Council must not remain silent. The council can and must act and it should do so without further delay."
The Security Council met on Saturday after Israel sent in ground troops to Gaza following a week of air strikes, but failed to agree a statement that would have called for immediate ceasefire.
Smart said the council had a "key responsibility to help ensure that the parties to the conflict respect international human rights and humanitarian law".
"It is imperative that the council urgently adopt a strong resolution condemning attacks against civilians by both Israel and Hamas and demanding that such attacks cease immediately," he said.
Amnesty also called for the Security Council to urge Israel to lift restrictions on the passage of humanitarian aid into Gaza, and to consider the deployment of international monitors to the territory.
The Palestinian death toll rose to 550 on Monday, medics in Gaza said, as Israeli troops battled Hamas fighters in Gaza's main city for the first time, while the Jewish state's government rejected calls for a ceasefire.