TEL AVIV, Israel — The Israeli military says it has launched a new ground offensive in Gaza, sending troops back into areas they had retreated from during a nearly two-month ceasefire. This comes a day after Israel broke the ceasefire with a punishing series of airstrikes that killed more than 400 people, many of whom were children, and wounded hundreds more.

The IDF said it aims to expand what it calls the “security perimeter” separating Gaza and Israel, and to create a “partial buffer zone” between the north and south of the Gaza Strip. The IDF says it has “taken control and re-established” its presence in the Netzarim corridor, the large strip of land dividing Gaza’s north and south that troops had occupied during the war and retreated from as part of a January ceasefire agreement.