A two-hour humanitarian ceasefire on Sunday, agreed by both sides, broke down within minutes
The head of the Cairo-based Arab League, Nabil el-Araby, described Israeli attacks on Gaza that killed at least 60 Palestinians on Sunday as a "war crime".
Palestinian witnesses and officials said at least 62 Palestinians were killed in shelling of a Gaza neighbourhood that left bodies strewn in the streets and thousands fleeing for shelter.
The Israeli military said militants from Gaza's dominant Hamas group responded with anti-tank missiles and heavy weapon fire in some of the bloodiest fighting since Israel launched its Gaza offensive 13 days ago.
"El-Araby (...) considered Israel's terrible shelling and ground attack operations in the neighbourhood of Shejaia as a war crime against Palestinian civilians and a dangerous escalation," the Arab League said in a statement on Sunday.
Israel says its air strikes, naval barrages and ground assault in Gaza, controlled by Islamist group Hamas, aim to halt rockets fired into Israeli territory. Analysts say its estimates of the size of Hamas' remaining arsenal will be a key factor in its deliberations on how long to continue the offensive.
A two-hour humanitarian ceasefire in the area on Sunday, agreed by both sides at the request of the International Committee of the Red Cross, broke down within minutes with each side blaming the other.