UN Security General Ban Ki-moon has appealed for a ceasefire between Israel and Palestinian militants in Gaza.
He urged both sides to exercise restraint, saying the Middle East could not afford "another full-blown war".
More than 80 Palestinians have been killed since Israel's operation began on Tuesday.
Israel says it has hit more than 100 targets in Gaza since midnight, while Palestinian militants are continuing to fire rockets into Israel.
The UN Security Council will meet later to discuss the crisis between Israel and the militant group Hamas.
